Agenda - Planning Commission - 08/08/2005

Home

number of units. A study of Seattle:area households found that a home on a 6,5oo- square-foot lot uses 6o percent less water than one on a t6,ooo-foot lot. Large lot size also increases the length of the pipes needed to serve households and commercial buildin§s, and §renter length means ~reater costs. A recent study in the Journal of the Arnericun Planning Association used an en§i- neerin§ cost model to assess the influence of land use on the cost of water distribution and sewer services. The study estimated annual water costs at $14.3 for a household located on a o.25-acre lot in a compact development ne[ir the water supply plant. If the household moved to a one-acre lot in a similar location, its annual water costs would be $272, even if the house- hold maintained the same water usage. If that same household used the same amount of water on a one-acre site in a dispersed develop- ment far from the service center, its water serv- ice would cost $388 annually. Because this coml]arison assumes all households use the same ~]mount of water, the difference reflects only the cost of infrastructure and pumpin§ and not the cost of water consumption for the lar§er lawns nn lar§er lots, The ]APA study found that infrastructure and pumping cost.~ of water service are more sensitive to lot size than any other factor. The principal reason for this difference is that longer distribution mains are required to distribute water from transmission mains under the lot and im:o the home. Costs for transmission mains that transmit water from the plant to the development are more expensive for developments farther away from the water supply source, but transmis- sion mains accounted for an average of only 16 percent of the total infrastructure and pumping costs. In Costs of Sprawl, published in 2000 by the National Research Council, fiscal impact analysis expert Robert Burchell and a team of researchers at Rut§ers University developed detailed national models and estimates of infra- structure costs under a "business as usual" approach and more compact development. Burchell estimates that more compact growth nationwide would save $4.77 billion, or 6.5 per- cent of total water infrastructure costs, from ~ooo to 2o25. The saving's would be parti(iularly si§nificant in southern and western areas of the U,S., where growth is greatest. LEAKAGE All water systems leak through pipes and at joints. Oepending on the condition of the infrastructure, a drinking water system can . lose from 6 percent to more than 25 percent of its water through leaks and breaks. Longer systems leak more than shorter ones, and less compact communities require longer systems. As development moves into iow-density areas, communities continue to build water systems that are inherently more prone to (eaka§e over time. System pressure also contribu'tes to leak- age, and those operating' at higher pressures over longer periods leak more. Systems in Iow- density areas must use higher.pressures to push water through longer mafns. Because Iow-density areas tend to have a higher water demand for lawns, dry months require pres- sure increases. When the central pumping sta- tion sits on the urban fringe, nearby Iow-den- sity users leak les~s than more distant users. Nonetheless, highly dispersed communities incur greater losses overall than do more com- pact communities with centrally located water service centers. The amount of water lost to leaks is diffi- cult to measure and varies widely among indi- vidual systems. Reliable national estimates of leakage are'rare, but operators of local sys- tems put greater emphasis on eliminating leaks now that water scarcity is a real and present threat. The Kansas Water Authority articulates the problem well: Lost water is host money .... If losses are caused by leaks, you've lost the money it cost to produce or purchase that water. In some cases, curbin§ lar§e water losses from leaks can save a town or district the cost of findin§ additional water sources. Wasted water means wasted dalJars. ZONING PRACTICE 5.05