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3 Quantities Available for Beneficial Use and Potential Impacts on Water Demand
Pages 39-61

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From page 39...
... . Use of graywater for toilet flushing alone would Graywater can be reused in the residential setting, at reduce indoor water demand on average by 24 percent.
From page 40...
... per average water savings of 63 gphd in water demand are posmonth was observed (City of Long Beach, 2013)
From page 41...
... : Graywater and supplemental Water Demand potable water as needed is used to irrigate turfgrass to barely meet the evapotranspiration deficit (see Box To examine potential potable water savings from gray- 3-1)
From page 42...
... Potable de mand for outdoor irrigation is unchanged from the base scenario. The typical household produces more graywater per day than is needed to meet toilet flushing demand, and therefore total indoor potable water demand was reduced by 11 gpcd multiplied by the population (1,200)
From page 43...
... On the contrary, using graywater for irripercent potable water savings, although only 17 percent of gation results in evapotranspiration losses and is considered the minimum irrigation demand for turfgrass in Los Angeles a consumptive use of water. If existing landscape irrigation is met through graywater reuse in the irrigation-only scenar- with potable water is replaced with graywater, then the propio.
From page 44...
... Most individuals irrigate at rates much higher than the conservation irrigation rates assumed in this analysis, which may underestimate potential potable water savings in locations having moderate to large rainfall amounts. However, water conservation trends may also impact water savings.
From page 45...
... TABLE 3-1 Potential Potable Water Savings in Six Cities from Various Graywater Use Scenarios Based on a 100-Acre, Medium-Density, Residential Area Volume Potable Water Savings Potable Water Savings S3: Irrigation S3: Irrigation Base demand S1: Irrigation S2: Toilet flushing and toilet flushing S1: Irrigation S2: Toilet and toilet (Mgal/yr) use only (Mgal/yr)
From page 46...
... Commercial Use Graywater and Water Conservation. The committee's estimates of potential potable water savings associated with the In general, commercial water use is highly variable use of graywater (Figure 3-3)
From page 47...
... . When graywater is used for toilet flushing, potable water demand is reduced by the amount of graywater used for flushing.
From page 48...
... On-site the results of an original analysis to approximate potential laundry machines in offices, hotels, and other commercial water savings from household-scale stormwater capture for facilities may result in enough graywater generation to ren- various uses in medium-density, residential development in der reuse feasible. In this same study, 79 percent of water six different locations in the United States.
From page 49...
... of roof runoff would be produced from a typical 1,500 median rainfall of about 43 inches (110 cm) of rainfall ft2 (140 m2)
From page 50...
... hourly rainfall data supplied by EarthInfo (Santa Monica, California) (5-year periods, depending on completeness of rain record: all were from 1995 through 1999, except for the Lincoln calculations, which were from 1996 through 1999 due to many missing 1995 rainfall records)
From page 51...
... However, the extent to which conventional water (e.g., percentage landscaped area [needed for irrigation demand can be reduced will depend upon the amount of stor- calculations] and roof area [needed for runoff quantiage provided, the water demand, and the timing of rainfall ties]
From page 52...
... For example, the Southeast and East Coast have a greater abundance of larger rains with more runoff from landscaped areas in rela tionship to impervious areas. SOURCE: Source areas from the standard land use files used by the nonpoint source section of the Wisconsin Department of Natural Resources as maintained by the U.S.
From page 53...
... As in the graywater analysis, the committee considered The capacity to capture and use stormwater at the build- two beneficial uses of on-site nonpotable water -- irrigation ing scale is strongly dependent upon storage tank size. The and toilet flushing.
From page 54...
... See Appendix A for methods used to derive these data. TABLE 3-6 Potential Potable Water Savings in Six Cities Based on a 100-Acre, Medium-Density, Residential Area Using Two 35-gallon Rain Barrels per Household Volume Potable Water Savings Potable Water savings S3: Irrigation Base use S1: Irrigation use S2: Toilet and toilet flushing S1: Irrigation S2: Toilet S3: Irrigation and (Mgal/yr)
From page 55...
... Compared The maximum potential potable water savings is about 24 TABLE 3-7 Potential Potable Water Savings in Six Cities Based on a 100-Acre, Medium-Density, Residential Area Using One 2,200-gallon Stormwater Tank per Household Volume Potable Water Savings Potable Water Savings S3: Irrigation Base use S1: Irrigation use S2: Toilet and toilet flushing S1: Irrigation S2: Toilet S3: Irrigation and (Mgal/yr) only (Mgal/yr)
From page 56...
... flushing (%) toilet flushing (%)
From page 57...
... Figure 3-11 shows the effects of increasing water stor- tank size is dependent upon local climate conditions, stormage tank sizes on the annual domestic water savings based water runoff area relative to on-site water demands, site conon simulated capture of rooftop runoff in medium-density, ditions, overall objectives, costs, and benefits (see Chapter residential areas in Los Angeles. In this case, all of the an- 7)
From page 58...
... Again, because of the nature of these analyses using multi- Overall, the potential water savings from neighborhoodyear modeling, some years will have greater benefits than scale stormwater capture is related to the available stormthese estimates, while other years will have smaller benefits. water storage volume and the groundwater infiltration rate, source area, land development types, and correlation of waOther Land Uses.
From page 59...
... Un3-4 provide more than enough water to meet medium-den- der wetter East Coast and Southeast conditions, stormwater at sity, residential toilet flushing (48,000 gallons/yr/acre) and a regional scale could supply at least twice the water demand irrigation needs (150,000 gallons/yr/acre [1,400 m3/yr/ha or for indoor use, providing sufficient additional water for ir450 m3/yr/ha]
From page 60...
... Use of storm- conservation irrigation of turfgrass, toilet flushing, or both, water for irrigation results in the same water losses to the hy- as well as other assessments of potable water savings in the drologic cycle from consumptive use because of evapotrans- literature. The committee's analyses primarily focused on piration and recharge to groundwater, as would have been on-site capture and use of graywater or stormwater at the the case for potable water applied to existing landscaping medium-density, residential scale, using 1994-1999 prethat the stormwater replaced.
From page 61...
... which stormwater can be stored in aquifers for use during Although use of graywater or roof runoff for toilet flushing drought or the dry season. The committee's scenario analy- can reduce indoor demand by up to 24 percent, the potential ses showed that average 1995-1999 stormwater runoff for annual reduction in domestic water demand for the Los Anmedium-density, residential developments in Los Angeles geles area estimated in the committee's scenario analyses avwould be roughly sufficient to meet indoor, residential, water eraged only 13 percent for graywater reuse (and significantly needs in those areas.


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