Concerns about public health are the biggest obstacles in legalizing graywater use. The quality varies depending on how it was used. Water from washing diapers, for example, will probably be more contaminated than water from a shower. Fecal coliform bacteria levels and nitrates have been of particular concern, although the threat is perhaps exaggerated. Salmonella and polio virus have been shown to last several days in graywater. Data accurately characterizing factors that determine graywater quality and assessing risks of use is limited. Studies are needed to develop guidelines for the safe reuse of residential graywater. The Water Conservation Alliance of Southern Arizona (Water CASA), in cooperation with ADWR, ADEQ and Pima County Department of Environmental Quality, is studying residential graywater reuse in Tucson. Study results will help determine if health risks increase with graywater reuse, and whether permitting standards can be loosened.

Graywater reuse has limited potential for helping TAMA reach safe yield. For the 85 to 90 percent of homes connected to the central sewage system, water used as graywater does not enter the sewage system to be treated for reuse or discharged to the Santa Cruz River. About 96 percent of the treated water that is released into the Santa Cruz River recharges the aquifer in TAMA. The use of water at a domestic site rather than treated and used someplace else gets us no closer to TAMA-wide safe yield.

However, residential graywater reuse can be an effective tool to better manage our groundwater by matching water quality to the actual quality needed for a particular water use. Residential graywater reuse reduces the demand for groundwater. Less water will then be withdrawn from areas of serious water table declines, such as Tucson’s Central Wellfield. Graywater reuse also saves the cost of moving groundwater through the water system, from disinfection to delivery to eventual sewage treatment. Further, a sizeable reduction in the waste stream going to the treatment plant could reduce its operating and capital expenses and delay the need for expanding those facilities.

RESIDENTIAL WATER USE

Pima County’s population is projected to increase from today’s figure of about 836,000 to 1.3 million by the year 2025. Most of that growth is expected to occur in the Tucson metropolitan area. As the population grows, total water use will increase.

If per capita water use rates stay about the same as today, total municipal water demand would increase from 172,900 acre-feet in 2000 to 267,100 acre-feet in 2025. The water saving potential of both new and existing housing must be examined for appropriate ways for a diverse population living in varied housing to conserve water.

Figure 5-6 Typical single family home indoor water use.Source: Data is a copyright of the American Water Works Association and were compiled for WaterWiser, www.waterwiser.org, by John Olaf Water Resources Management.

Water can be conserved both indoors and outdoors. Most of the water used indoors winds up in a sanitary sewer or septic system. For homes hooked up to the sewer system, water used indoors is re-used or recharges the aquifer. Much of the water used outdoors evaporates and leaves TAMA. Therefore, saving water outdoors has a greater effect on the total water budget for the Tucson area than does saving water indoors. Saving water indoors, however, does reduce the cost of transporting water to the treatment plant and treating it.

It is important to note, however, that given Tucson’s projected population growth, no level of water conservation, even if involving all types of water users, will be sufficient to ensure a balanced water budget.

Indoor Water Use

Indoor uses remain fairly constant throughout the year. People may wash more clothes in the summer, but in the winter the bulk of clothes washed is greater. Similarly, other indoor water uses vary little during the course of the year. This constancy is reflected in relatively flat levels of sewage water flow.

Figure 5-6 shows that the largest indoor uses of water are toilets, showers and baths, and washing machines in all types of housing. Newer models of toilets are designed to use less water than older models. Until the early 1980s, most new toilets used five to seven gallons per flush. Water-conserving 3.5 gallons per flush toilets were the standard until the early 1990s when 1.6-gallon ultra low flush () toilets became available. In 1989, both Tucson and County adopted ordinances requiring installation of ULF toilets in new construction.

Replacing older toilets with ULF toilets is one of the best ways to save water indoors. ULF toilet savings do not require a change in behavior and, if the toilet continues to function properly, will effectively save water. However, while many models of ULF toilets function very well, recent anecdotal evidence indicates that some models of ULF toilets deteriorate over time. Further, replacement parts are not readily available for some models, forcing homeowners to find alternative parts that can negate the water saving feature of the toilet. Other people continue to use ULF toilets without making repairs; this also results in less water savings. The University of Arizona’s Water Resources Research Center is conducting a study to identify the extent of this problem and to determine which models of ULF toilet have not held up over time. This information can be used to rewrite plumbing codes, upgrade ULF toilet quality, and make the correct replacement parts easier to obtain.

Toilet dams and other water displacement devices can help save water in older model toilets. Toilet dams, which are placed in the tank to keep water from fully filling the tank, typically save about one gallon per flush. Water-filled bags or plastic bottles also can be used in place of dams and typically save about the same amount.

Showers and baths are another large component of indoor water use. Showers and baths typically comprise about 20 to 25 percent of total indoor water use in older homes. Low-flow shower heads also can save water. Older shower heads typically use 3.5 gallons per minute (gpm), while low-flow shower heads typically use 2.5 gpm or less.

Clothes washers typically account for between 20 and 25 percent of indoor water use. Clothes washers vary widely in their water use. Older models used about 55 gallons per load, while more water-efficient models use around 42 gallons per load. Newer, more efficient models, including horizontal axis machines, use about 30 gallons per load.