How to Conserve Water and Use It Effectively

Water users can be divided into two basic groups: system users (such as residential users, industries, and farmers) and system operators (such as municipalities, state and local governments, and privately owned suppliers). These users can choose from among many different water use efficiency practices, which fall into two categories:

1. Engineering practices: practices based on modifications in plumbing, fixtures, or water supply operating procedures
2. Behavioral practices: practices based on changing water use habits

This chapter explores a number of water use efficiency practices. The practices have been evaluated by many researchers, and there is a growing body of literature that presents the results of many studies related to water use efficiency.

This chapter addresses the following questions: What's the problem? What practices might be used to solve it? How effective are they? What do they cost? Where have they been used successfully? Practices for system users residential, industrial/commercial, and agricultural are presented first, followed by practices for system operators.

Practices for Residential Users

The following sections present examples of conservation and water use efficiency practices that can benefit residential users. Both engineering and behavioral practices are described.

Engineering Practices

Plumbing

An engineering practice for individual residential water users is the installation of indoor plumbing fixtures that save water or the replacement of existing plumbing equipment with equipment that uses less water. Low-flow plumbing fixtures and retrofit programs are permanent, one-time conservation measures that can be implemented automatically with little or no additional cost over their life times (Jensen, 1991). In some cases, they can even save the resident money over the long term.

The City of Corpus Christi, for example, has estimated that an average three-member household can reduce its water use by 54,000 gallons annually and can lower water bills by about $60 per year if water-efficient plumbing fixtures are used (Jensen, 1991). Further support for this conclusion is provided below.

Low-Flush Toilets. Residential demands account for about three-fourths of the total urban water demand. Indoor use accounts for roughly 60 percent of all residential use, and of this, toilets (at 3.5 gallons per flush) use nearly 40 percent. Toilets, showers, and faucets combined represent two-thirds of all indoor water use. More than 4.8 billion gallons of water is flushed down toilets each day in the United States. The average American uses about 9,000 gallons of water to flush 230 gallons of waste down the toilet per year (Jensen, 1991). In new construction and building rehabilitation or remodeling there is a great potential to reduce water consumption by installing low-flush toilets.

Conventional toilets use 3.5 to 5 gallons or more of water per flush, but low-flush toilets (see figure above) use only 1.6 gallons of water or less. Since low-flush toilets use less water, they also reduce the volume of wastewater produced (Pearson, 1993).

Effective January 1, 1994, the Energy Policy Act of 1992 (Public Law 102-486) requires that all new toilets produced for home use must operate on 1.6 gallons per flush or less (Shepard, 1993). Toilets that operate on 3.5 gallons per flush will continue to be manufactured, but their use will be allowed for only certain commercial applications through January l, 1997 (NAPHCC, 1992).

Even in existing residences, replacement of conventional toilets with low-flush toilets is a practical and economical alternative. The effectiveness of low-flush toilets has been demonstrated in a study in the City of San Pablo, California. In a 30-year-old apartment building, conventional toilets that used about 4.5 gallons per flush were replaced with low-flush toilets that use approximately 1.6 gallons per flush. The change resulted in a decrease in water consumption from approximately 225 gallons per day per average household of 3® persons to 148 gallons per day per household a savings of 34 percent! Although the total cost for replacement of the conventional toilets with low-flush toilets was about $250 per unit (including installation), the water conservation fixtures saved an average of $46 per year from each unit's water bill. Therefore, the cost for the replacement of the conventional toilet with a low-flush toilet could be recovered in 5.4 years.

Toilet Displacement Devices. Plastic containers (such as plastic milk jugs) can be filled with water or pebbles and placed in a toilet tank to reduce the amount of water used per flush. By placing one to three such containers in the tank (making sure that they do not interfere with the flushing mechanisms or the flow of water), more than l gallon of water can be saved per flush. A toilet dam, which holds back a reservoir of water when the toilet is flushed, can also be used instead of a plastic container to save water. Toilet dams result in a savings of 1 to 2 gallons of water per flush (USEPA, l991b).

Low-Flow Showerheads. Showers account for about 20 percent of total indoor water use. By replacing standard 4.5-gallon-per-minute showerheads with 2.5-gallon-per-minute heads, which cost less than $5 each, a family of four can save approximately 20,000 gallons of water per year (Jensen, 1991). Although individual preferences determine optimal shower flow rates, properly designed low-flow showerheads are available to provide the quality of service found in higher-volume models.

Whitcomb (1990) developed a model to estimate water use savings resulting from the installation of low-flow showerheads in residential housing. Detailed data from 308 single-family residences involved in a pilot program in Seattle, Washington, were analyzed. The estimated indoor water use per person dropped 6.4 percent after low-flow showerheads were installed (Whitcomb, 1990).

Faucet Aerators. Faucet aerators, which break the flowing water into fine droplets and entrain air while maintaining wetting effectiveness, are inexpensive devices that can be installed in sinks to reduce water use. Aerators can be easily installed and can reduce the water use at a faucet by as much as 60 percent while still maintaining a strong flow. More efficient kitchen and bathroom faucets that use only 2 gallons of water per minute--unlike standard faucets, which use 3 to 5 gallons per minute--are also available (Jensen, 1991).

Pressure Reduction. Because flow rate is related to pressure, the maximum water flow from a fixture operating on a fixed setting can be reduced if the water pressure is reduced. For example, a reduction in pressure from 100 pounds per square inch to 50 psi at an outlet can result in a water flow reduction of about one-third (Brown and Caldwell, 1984).

Homeowners can reduce the water pressure in a home by installing pressure-reducing valves. The use of such valves might be one way to decrease water consumption in homes that are served by municipal water systems. For homes served by wells, reducing the system pressure can save both water and energy. Many water use fixtures in a home, however, such as washing machines and toilets, operate on a controlled amount of water, so a reduction in water pressure would have little effect on water use at those locations.

A reduction in water pressure can save water in other ways: it can reduce the likelihood of leaking water pipes, leaking water heaters, and dripping faucets. It can also help reduce dishwasher and washing machine noise and breakdowns in a plumbing system.

A study in Denver, Colorado, illustrates the effect of water pressure on water savings. Water use in homes was compared among different water pressure zones throughout the city. Elevation of a home with respect to the elevation of a pumping station and the proximity of the home to the pumping station determine the pressure of water delivered to each home. Homes with high water pressure were compared to homes with low water pressure. An annual water savings of about 6 percent was shown for homes that received water service at lower pressures when compared to homes that received water services at higher pressures.

Gray Water Use. Domestic wastewater composed of wash water from kitchen sinks and tubs, clothes washers, and laundry tubs is called gray water (USEPA, 1989). Gray water can be used by homeowners for home gardening, lawn maintenance, landscaping, and other innovative uses. The City of St. Petersburg, Florida, has implemented an urban dual distribution system for reclaimed water for nonpotable uses. This system provides reclaimed water for more than 7,000 residential homes and businesses (USEPA, 1992).

Landscaping

Lawn and landscape maintenance often requires large amounts of water, particularly in areas with low rainfall. Outdoor residential water use varies greatly depending on geographic location and season. On an annual average basis, outdoor water use in the arid West and Southwest is much greater than that in the East or Midwest. Nationally, lawn care accounts for about 32 percent of the total residential outdoor use. Other outdoor uses include washing automobiles, maintaining swimming pools, and cleaning sidewalks and driveways.

Landscape Irrigation. One method of water conservation in landscaping uses plants that need little water, thereby saving not only water but labor and fertilizer as well (Grisham and Fleming, 1989). A similar method is grouping plants with similar water needs. Scheduling lawn irrigation for specific early morning or evening hours can reduce water wasted due to evaporation during daylight hours. Another water use efficiency practice that can be applied to residential landscape irrigation is the use of cycle irrigation methods to improve penetration and reduce runoff. Cycle irrigation provides the right amount of water at the right time and place, for optimal growth. Other practices include the use of low-precipitation-rate sprinklers that have better distribution uniformity, bubbler/soaker systems, or drip irrigation systems (RMI, 1991).

Xeriscape Landscapes. Careful design of landscapes could significantly reduce water usage nationwide. Xeriscape landscaping is an innovative, comprehensive approach to landscaping for water conservation and pollution prevention. Traditional landscapes might incorporate one or two principles of water conservation, but xeriscape landscaping uses all of the following: planning and design, soil analysis, selection of suitable plants, practical turf areas, efficient irrigation, use of mulches, and appropriate maintenance (Welsh et al., 1993).

Benefits of xeriscape landscaping include reduced water use, decreased energy use (less pumping and treatment required), reduced heating and cooling costs because of carefully placed trees, decreased storm water and irrigation runoff, fewer yard wastes, increased habitat for plants and animals, and lower labor and maintenance costs (USEPA, 1993).

More than 40 states have initiated xeriscape projects. Some communities use contests and demonstration gardens to promote public awareness. El Paso Water Utilities and the Council of El Paso Garden Clubs sponsor an annual "Accent Sun Country" contest. The contest spotlights homes that have water-conserving landscapes consisting of plants and grasses that require only a minimum of supplemental water and yet beautify the homes. The winning entries are publicized, and cash prizes are awarded. People are invited to tour the grounds to get ideas on how they, too, can save water, time, and money while maintaining an attractive landscape (RMI, 1991). The offices of the Southwest Florida Water Management District in Tampa and Brooksville offer free xeriscape tours every month. The tours begin with a slide show on the principles of xeriscape and continue with a walking tour of water-saving landscaping (Xeriscape tours, 1993).

Behavioral Practices

Behavioral practices involve changing water use habits so that water is used more efficiently, thus reducing the overall water consumption in a home. These practices require a change in behavior, not modifications in the existing plumbing or fixtures in a home. Behavioral practices for residential water users can be applied both indoors in the kitchen, bathroom, and laundry room and outdoors.

In the kitchen, for example, 10 to 20 gallons of water a day can be saved by running the dishwasher only when it is full. If dishes are washed by hand, water can be saved by filling the sink or a dishpan with water rather than running the water continuously. An open conventional faucet lets about 5 gallons of water flow every 2 minutes (Florida Commission, 1990).

Water can be saved in the bathroom by turning off the faucet while brushing teeth or shaving. Water can be saved by taking short showers rather than long showers or baths and turning the water off while soaping. This water savings can be increased even further by installing low-flow showerheads, as discussed earlier. Toilets should be used only to carry away sanitary waste.

Households with lead-based solder in pipes that flush the first several gallons of water should collect this water for alternative nonpotable uses (e.g., plant watering).

Water can be saved in the laundry room by adjusting water levels in the washing machine to match the size of the load. If the washing machine does not have a variable load control, water can be saved by running the machine only when it is full. If washing is done by hand, the water should not be left running. A laundry tub should be filled with water, and the wash and rinse water should be reused as much as possible.

Outdoor water use can be reduced by watering the lawn early in the morning or late in the evening and on cooler days, when possible, to reduce evaporation. Allowing the grass to grow slightly taller will reduce water loss by providing more ground shade for the roots and by promoting water retention in the soil. Growing plants that are suited to the area ("indigenous" plants) can save more than 50 percent of the water normally used to care for outdoor plants.

As much as 150 gallons of water can be saved when washing a car by turning the hose off between rinses. The car should be washed on the lawn if possible to reduce runoff.

Additional savings of water can result from sweeping sidewalks and driveways instead of hosing them down. Washing a sidewalk or driveway with a hose uses about 50 gallons of water every 5 minutes (Florida Commission, 1990). If a home has an outdoor pool, water can be saved by covering the pool when it is not in use.

Practices for Industrial/Commercial Users

Industrial/commercial users can apply a number of conservation and water use efficiency practices. Some of these practices can also be applied by users in the other water use categories.

Engineering Practices

Water Reuse and Recycling

Water reuse [BROKEN] is the use of wastewater or reclaimed water from one application such as municipal wastewater treatment for another application such as landscape watering. The reused water must be used for a beneficial purpose and in accordance with applicable rules (such as local ordinances governing water reuse). Some potential applications for the reuse of wastewater or reclaimed water include other industrial uses, landscape irrigation, agricultural irrigation, aesthetic uses such as fountains, and fire protection (USEPA, 1992). Factors that should be considered in an industrial water reuse program include (Brown and Caldwell, 1990):

• Identification of water reuse opportunities
• Determination of the minimum water quality needed for the given use
• Identification of wastewater sources that satisfy the water quality requirements
• Determination of how the water can be transported to the new use

The reuse of wastewater or reclaimed water is beneficial because it reduces the demands on available surface and ground waters (Strauss, 1991). Perhaps the greatest benefit of establishing water reuse programs is their contribution in delaying or eliminating the need to expand potable water supply and treatment facilities (USEPA, 1992). Water recycling [BROKEN] is the reuse of water for the same application for which it was originally used. Recycled water might require treatment before it can be used again. Factors that should be considered in a water recycling program include (Brown and Caldwell, 1990):

• Identification of water reuse opportunities
• Evaluation of the minimum water quality needed for a particular use
• Evaluation of water quality degradation resulting from the use
• Determination of the treatment steps, if any, that might be required to prepare the water for recycling

Cooling Water Recirculation

The use of water for cooling in industrial applications represents one of the largest water uses in the United States. Water is typically used to cool heat-generating equipment or to condense gases in a thermodynamic cycle. The most water-intensive cooling method used in industrial applications is once-through cooling, in which water contacts and lowers the temperature of a heat source and then is discharged.

Recycling water with a recirculating cooling system can greatly reduce water use by using the same water to perform several cooling operations. The water savings [BROKEN]are sufficiently substantial to result in overall cost savings to the industry (see box). Three cooling water conservation approaches that can be used to reduce water use are evaporative cooling, ozonation, and air heat exchange (Brown and Caldwell, 1990).

In industrial/commerical evaporative cooling systems, water loses heat when a portion of it is evaporated. Water is lost from evaporative cooling towers as the result of evaporation, drift, and blowdown. (Blowdown is a process in which some of the poor-quality recirculating water is discharged from the tower in order to reduce the total dissolved solids.) Water savings associated with the use of evaporative cooling towers can be increased by reducing blowdown or water discharges from cooling towers.

The use of ozone to treat cooling water (ozonation) can result in a five-fold reduction in blowdown when compared to traditional chemical treatments and should be considered as an option for increasing water savings in a cooling tower (Brown and Caldwell, 1990).

Air heat exchange works on the same principle as a car's radiator. In an air heat exchanger, a fan blows air past finned tubes carrying the recirculating cooling water. Air heat exchangers involve no water loss, but they can be relatively expensive when compared with cooling towers (Brown and Caldwell, 1990).

The Pacific Power and Light Company's Wyodak Generating Station in Wyoming decided to use dry cooling to eliminate water losses from cooling-water blowdown, evaporation, and drift. The station was equipped with the first air-cooled condenser in the western hemisphere. Steam from the turbine is distributed through overhead pipes to finned carbon steel tubes. These are grouped in rectangular bundles and installed in A-frame modules above 69 circulating fans. The fans force some 45 million cubic feet per minute (ft3/min) of air through 8 million square feet of finned-tube surface, condensing the steam (Strauss, 1991).

The payback comes from the water savings. Compared to about 4,000 gallons per minute (gal/min) of makeup (replacement water) for equivalent evaporative cooling, the technique reduces the station's water requirement to about 300 gal/min (Strauss, 1991).

Rinsing [BROKEN]

Another common use of water by industry is the application of deionized water for removing contaminants from products and equipment. Deionized water contains no ions (such as salts), which tend to corrode or deposit onto metals. Historically, industries have used deionized water excessively to provide maximum assurance against contaminated products. The use of deionized water can be reduced without affecting production quality by eliminating some plenum flushes (a rinsing procedure that discharges deionized water from the rim of a flowing bath to remove contaminants from the sides and bottom of the bath), converting from a continuous-flow to an intermittent-flow system, and improving control of the use of deionized water (Brown and Caldwell, 1990).

Deionized water can be recycled after its first use, but the treatment for recycling can include many of the processes required to produce deionized water from municipal water. The reuse of once-used deionized water for a different application should also be considered by industry, where applicable, because deionized water is often more pure after its initial use than municipal water (Brown and Caldwell, 1990).

Landscape Irrigation

Another way that industrial/commercial facilities can reduce water use is through the implementation of efficient landscape irrigation practices. There are several general ways that water can be more efficiently used for landscape irrigation, including the design of landscapes for low maintenance and low water requirements (refer to the previous section on xeriscape landscaping), the use of water-efficient irrigation equipment such as drip systems or deep root systems, the proper maintenance of irrigation equipment to ensure that it is working properly, the distribution of irrigation equipment to make sure that water is dispensed evenly over areas where it is needed, and the scheduling of irrigation to ensure maximum water use (Brown and Caldwell, 1990). For additional information on efficient water use for irrigation, refer to the practices for residential users and agricultural users in this chapter.

Behavioral Practices

Behavioral practices involve modifying water use habits to achieve more efficient use of water, thus reducing overall water consumption by an industrial/commercial facility. Changes in behavior [BROKEN] can save water without modifying the existing equipment at a facility.

Monitoring the amount of water used by an industrial/commercial facility can provide baseline information on quantities of overall company water use, the seasonal and hourly patterns of water use, and the quantities and quality of water use in individual processes. Baseline information on water use can be used to set company goals and to develop specific water use efficiency measures. Monitoring can make employees more aware of water use rates and makes it easier to measure the results of conservation efforts. The use of meters on individual pieces of water-using equipment can provide direct information on the efficiency of water use. Records of meter readings can be used to identify changes in water use rates and possible problems in a system (Brown and Caldwell, 1990).

Many of the practices described in the section for residential users can also be applied by commercial users. These include low-flow fixtures, water-efficient landscaping, and water reuse and recycling (e.g., using recycled wash water for pre-rinse).

Practices for Agricultural Users

Engineering Practices

Irrigation

Water-saving irrigation practices fall into three categories: field practices, management strategies, and system modifications. Field practices are techniques that keep water in the field, distribute water more efficiently across the field, or encourage the retention of soil moisture. Examples of these practices include the chiseling of extremely compacted soils, furrow diking to prevent runoff, and leveling of the land to distribute water more evenly. Typically, field practices are not very costly.

Management strategies involve monitoring soil and water conditions and collecting information on water use and efficiency. The information helps in making decisions about scheduling applications or improving the efficiency of the irrigation system. The methods include measuring rainfall, determining soil moisture, checking pumping plant efficiency, and scheduling irrigation.

System modifications require making changes to an existing irrigation system or replacing an existing system with a new one. Because system modifications require the purchase of equipment, they are usually more expensive than field practices and management strategies. Typical system modifications include adding drop tubes to a center pivot system, retrofitting a well with a smaller pump, installing surge irrigation, or constructing a tailwater recovery system (Kromm and White, 1990).

Water Reuse and Recycling

Agricultural irrigation represents approximately 40 percent of the total water demand nationwide. Given that high demand, significant water conservation benefits could result from irrigating with reused or recycled water.

Water reuse [BROKEN] is the use of wastewater or reclaimed water from one application for another application. Reused water must be used for a beneficial purpose and in accordance with applicable rules (USEPA, 1991a). Water recycling is the reuse of water for the same application for which it was originally intended.

Factors that should be considered in an agricultural water reuse program include:

• The identification of water reuse opportunities
• Determination of the minimum water quality needed for the given use
• Identification of wastewater sources that satisfy the water quality requirements
• Determination of how the water can be transported to the new use (Brown and Caldwell, 1990)

Water reuse for irrigation is already in widespread use in rural areas and is also applicable in areas where agricultural sites are near urban areas and can easily be integrated with urban reuse applications (USEPA, 1992).

Behavioral Practices

Behavioral practices involve changing water use habits to achieve more efficient use of water. Behavioral practices for agricultural water users can be applied to irrigation application rates and timing. Changes in water use behavior can be implemented without modifying existing equipment.

For example, better irrigation scheduling can result in a reduction in the amount of water that is required to irrigate a crop effectively. The careful choice of irrigation application rates and timing can help farmers to maintain yields with less water. In making scheduling decisions, irrigators should consider:

• The uncertainty of rainfall and crop water demand
• The limited water storage capacity of many irrigated soils
• The limited pumping capacity of irrigation systems
• Rising pumping costs as a result of higher energy prices

Local NRCS-Conservation Districts and Cooperative Extension Service offices can play an important role in promoting better irrigation scheduling. Accurate information on crop water use requires information on solar radiation and other weather variables that can be collected by local weather stations. An additional method that can be used to improve irrigation scheduling and might result in high returns is the use of equipment such as resistance blocks, tensiometers, and neutron probes to monitor soil moisture conditions to help in determining when water should be applied (Bosch and Ross, 1990).

Practices for System Operators

Engineering Practices

Metering

Metering. [BROKEN] The measurement of water use with a meter provides essential data for charging fees based on actual customer use. Billing customers based on their actual water use has been found to contribute directly to water conservation. Meters also aid in detecting leaks throughout a water system. In 1977, for example, Boston, Massachusetts, could not account for the use of 50 percent of the water in its municipal water system. After installing meters, the city identified leaks and undertook a vigorous leak detection program (Grisham and Fleming, 1989). Unaccounted-for water dropped to 36 percent after metering and leak detection programs were started.

Submetering. [BROKEN] Submetering is used in units such as apartments, condominiums, and trailer homes to indicate water use by those individual units; the entire complex of units is metered by the main supplier. Submetering of water use in apartment or business complexes makes it possible to bill tenants for the water that they actually use rather than for a percentage of the total water use for the complex. Submetering makes water users more aware of how much water they use and its cost, and tenants who conserve water can benefit from lower water use costs. Submetering is reported to reduce water usage by 20 to 40 percent (Rathnau, 1991).

Leak Detection

One way to detect leaks is to use listening equipment to survey the distribution system, identify leak sounds, and pinpoint the exact locations of hidden underground leaks. As mentioned in the previous section, metering can also be used to help detect leaks in a system.

An effective way to conserve water is to detect and repair leaks in municipal water systems. [BROKEN]  Repairing leaks controls the loss of water that water agencies have paid to obtain, treat, and pressurize. The early detection of leaks also reduces the chances that leaks will cause major property damage. When water leaks from a system before it reaches the consumer, water agencies lose revenue and incur unnecessary costs. Such costs should provide an incentive for system operators to implement a leak detection program.

Programs for finding and repairing leaks in water mains and laterals (conduits) might be cost-effective in spite of their high initial costs. Leak detection programs have been especially important in cities that have large, old, deteriorating systems (RMI, 1991).

Water Main Rehabilitation

A water utility can improve the management and rehabilitation of a water distribution network by using a distribution system database. Using the database can help to lower maintenance costs and can result in more efficient use of the water resource. The database can help the utility manager to set priorities and efficiently allocate rehabilitation funds (Habibian, 1992). A comprehensive database should include information on the following:

• The characteristics of the system's components, such as size, age, and material
• The condition of mains, such as corrosion
• Soil conditions or type
• Failure and leak records
• Water quality
• High/low pressure problems
• Operating records, such as pump and valve operations
• Customer complaints
• Meter data
• Operating and rehabilitation costs

Water Reuse

Another practice that should be considered by water system operators who operate publicly owned treatment works is the reuse of treated wastewater. As discussed earlier, water reuse [BROKEN] is the use of wastewater or reclaimed water from one application for another application. Some potential applications for water reuse include landscape irrigation, agricultural irrigation, aesthetic uses such as fountains, industrial uses, and fire protection (USEPA, l991a). These factors should be considered in a water reuse program:

• The identification of water reuse opportunities
• The determination of the minimum water quality needed for the given use
• The identification of wastewater sources that satisfy the water quality requirements
• The determination of how the water can be transported to the new use (Brown and Caldwell, 1990)

Well Capping

Well capping is the capping of abandoned artesian wells whose rusted casings spill water in a constant flow into drainage ditches. In Seminole County, Florida, state hydrologists estimate that 1,500 abandoned artesian wells are discharging 54 Mgal/d. To put that in perspective, utilities in Seminole County pump less than 40 Mgal/d. The cost to plug such wells is about $750 (1990 dollars) per well. The state legislature has required that all such wells be capped beginning in 1993 (Florida Commission, 1990).

Planning and Management Practices

In addition to engineering practices, system operators can use several other practices to conserve water or improve water use efficiency.

Pricing

Information and education promoting conservation do not appear to be effective by themselves in achieving a conservation goal without at the same time imposing significant price increases to provide a financial incentive to conserve water (Martin and Kulakowski, 1991). Customers use less water when they have to pay more for it and use more when they know they can afford it. However, most people consider water to be a "free good" and are not willing to pay higher prices that reflect the true costs associated with the water delivered to their homes. Rate structures have the advantage of avoiding the costs of overt regulation, restrictions, and policing while retaining a greater degree of individual freedom of choice for water customers.

Overall charges for water service increased at an average compound rate of 7 percent per year during the 1980s nearly double the rate of inflation (Russet and Woodcock, 1992). There is concern over "price gouging" due to increased water rates (Collinge, 1992). Some pricing has been objected to on the grounds that it can lead to a substantial excess of revenues over costs an excess that might be inequitable and, in some states, unconstitutional (Collinge, 1992).

Water utility managers must establish and design water rates that meet revenue requirements and are fair and equitable to all customer classes in the water system. This task involves the following procedures:

• Determination of the water utility's total annual revenue requirements for the period for which the rates are to be in effect
• Determination of service costs by allocation of the total annual revenue requirements to the basic water system cost components and distribution of these costs to the various customer classes in accordance with their service requirements
• Design of water rates to recover the cost of service from each class of customer (Mui et al., 1991)

Several price rate structuring alternatives are available for water system operators.

Increasing Block Rate, or Tiered, Pricing. Increasing block rate, or tiered, pricing reduces water use by increasing per-unit charges for water as the amount used increases. For example, the first volume of water (block) used is charged a base rate, the second block is charged the base rate plus a surcharge, and the third block is charged the base rate plus a higher surcharge. It is necessary to increase real prices significantly to overcome the effects of conservation (Martin and Kulakowski, l991).

For example, as the cost of water increased in Tucson, Arizona, residents used 33 percent less water between 1974 and 1980. A 10 percent increase in water rates provided about 3 percent more revenue while triggering a 7 percent reduction in use (Billings and Day, 1989). Using seasonal increasing block rate pricing during summer and winter months, to encourage year-round conservation, resulted in estimated water savings for the single-family residential class in Tucson of an average 2.23 Mgal/d during 1983-1986 (Cuthbert, 1989).

Decreasing Block Rate Pricing. Decreasing block rate prices reflect per-unit costs of production and delivery that go down as customers consume more water.

The monthly water use records of 101 customers were measured in a study of municipal water use in the city of Denton, Texas. Summer water use records from 1976 to 1980 during a decreasing block rate period were compared to summer use records from 1981 to 1985 during an increasing block rate period. It was found that the decreasing block rate scenario encouraged greater water use, whereas the increasing block rate scenario resulted in a reaction to the price increase and a corresponding decrease in water use (Nieswiadomy and Molina, 1989).

Time-of-Day Pricing. Time-of-day pricing charges users relatively higher prices during a utility's peak use periods. Because customers are sensitive to price increases, these charges curtail demand. Time-of-day pricing can cut generating capacity and reduce reliance on expensive secondary fuel sources (Sexton et al., 1989).

Water Surcharges. A water surcharge imposes a higher rate on excessive water use. The customer pays more money per gallon for water use that is considered higher-than-average.

Surcharges include unit surcharges, winter/ summer ratios, and alternative seasonal rates. The unit surcharge method establishes a threshold level for excess consumption based on average daily per capita or per-household consumption. A surcharge is imposed for all water use above that threshold level. For the winter/summer ratio, metered water use during the winter period is compared to consumption during the corresponding summer period, and a higher rate or surcharge is imposed for water consumption above the average winter use. Typically, an increase in usage of 14-20 percent occurs during the summer. Under an alternative seasonal rate structure, all water used during the summer or peak season is billed at a higher rate than that used during the other seasons. The increased rate is applied to all customers at all water-use levels (Schlette and Kemp, 1991).

Retrofit Programs

Retrofit programs are another tool system operators can use to promote water use efficiency practices. Retrofitting involves the replacement of existing plumbing equipment with equipment that uses less water. The most successful water-saving fixtures are those which operate in the same manner as the fixtures they are replacing--for example, toilet tank inserts, shower flow restrictors, and low-flow showerheads. (For more information, refer to the practices for residential users.) As discussed previously, retrofit programs are permanent, one-time conservation measures that can be implemented with little or no additional cost over their lifetimes (Jensen, 1991).

A retrofit program can involve the use of education programs to let users know which fixtures are best, where to get them, and how to install them. System operators can also purchase water-efficient fixtures and resell them at cost to the users, but the most successful retrofit programs have been those in which the system operator purchases, distributes, and installs the fixtures (AWWA, n.d.).

Retrofit programs have been shown to be cost-effective and useful in conserving water in many cases. An apartment building in New England with 151 units was retrofitted with low-flow showerheads and faucet aerators at a cost of $1,074. As a result of the retrofit 1,725,000 gallons of water, $8,590 for energy, and $980 for water were saved in 1 year (AWWA, n.d.). In another retrofit program, the Lower Colorado River Authority installed low-flow showerheads and toilet dams in an apartment complex and public housing program in Marble Falls, Texas. Indoor per capita water use was reduced by 21 percent (from 81 to 64 gal/cap/day) in the apartment complex and was reduced 11 percent (from 102 to 91 gal/cap/da