Water Planning for Growing Southwestern Communities - Design with the Desert: Conservation and Sustainable Development - page 272

groundwater-dependent community water systems (see Chapter 21). Outdoor watering
does not require highly treated water. Therefore, as communities find themselves faced
with expensive treatment options for potable water systems, separating indoor and
outdoor water systems make sense. Because the cost of retrofitting plumbing on older
buildings can be high, this may be more appropriate in areas of new construction. In 2008,
Tucson, Arizona, became the first city in the United States to require new commercial
buildings to rely on harvested rainwater for half of their outdoor watering needs, and
both New Mexico and Texas promote rainwater harvesting initiatives.* To the extent that
the rainwater is used to displace water delivered through the potable system, more use
of rainwater will reduce demands on the engineered systems communities use to deliver
water to their customers. It should be noted that the rules and regulations pertaining
to rainwater systems vary significantly by state. † For example, in Colorado, rainwater
harvesting is only allowed in rural areas. ‡
Gray water systems provide the opportunity for individual water users to recycle
their water and thereby reduce their demands on the potable water system. Widespread
installation of gray water systems must be factored into the design and operation of
wastewater collection and treatment systems. Existing wastewater collection systems rely
on outflows from washing machines and dishwashers. These flows provide water used to
move waste solids through the wastewater collection system to the treatment plants. In
Arizona, gray water systems require a valve so that users can either send the gray water
outflows to the sewage lines or divert them for on-premise use. § This customer choice
means that the flows to the wastewater treatment plant will not be as large or predictable as
historically has been the case. This may require changes to the long-range water resource
plans of community water systems. Lower demand on the potable system means less need
for new water sources in the future, reduced flows to the treatment facilities, and less
reclaimed water available to the community water system for turf facility or other uses.
More widespread use of treated effluent, particularly in planned communities and large
developments, will likely require smaller and more strategically located treatment plants
than the large-scale treatment plants built in the past.
15.3 Investments in Water Infrastructure
The discussion of treatment technology should highlight the fact that identifying and
paying for wet water supplies are not the only challenges associated with providing water to
growing urban areas. The infrastructure investments associated with treatment and deliv-
ery of the water supplies can be huge. Although there is limited discussion of new dams, ¶
transporting water from the Colorado River to the Navajo Nation or desalinated water
* See O'Dell, 17 The Texas Manual on Rainwater Harvesting, prepared by the Texas Water Development Board,
2005, and A waterwise guide to rainwater harvesting by the New Mexico Office of the State Engineer.
† See the student research paper by Lien. 18 Available from S.B. Megdal by request.
‡ See Johnson. 19
§ It will be interesting to measure, if possible, the changes in outdoor water use that result from installation of
gray water systems over time to see if the ready availability of flows from dishwashers and washing machines
is significant enough to lead to increased water use for landscape irrigation in semi-arid or arid areas. Data
are not often available to measure the effectiveness of water conservation approaches. See Megdal. 20
¶ Dams are still under consideration. See Schwarzenegger … 21 and Schultz. 22