This response from the Pacific Research Institute to a recent policy report puts it in perspective and, of course, the major solution to water supply issues related to growth is to increase water supply by increasing surface water storage, in addition to any technological or behavior adaptations that can be reasonably taken.
An excerpt.
...But Not a Drop to Drink
by Amy Kaleita, Public Policy Fellow, Environmental Studies, Pacific Research Institute
A recent report from the Public Policy Institute of California suggests that population growth in California's hot, dry, inland counties will put a strain on the state's water supply. The release of this report coincided with the USDA, in cooperation with the Irrigation Association, naming July "Smart Irrigation Month" to promote awareness of efficient irrigation. Unfortunately, the message that much of the media has been promoting from this report is not so smart.
For example, San Mateo County Times' Steve Geissinger writes, "In essence, the study indicates that it will likely come down to lawns in the Central Valley versus drinking water for the generally cooler but more populous Bay Area and Los Angeles regions." This is not likely.
California is hardly maxed out on water supply as it is, and while outdoor water use is a significant component of domestic water use, particularly in single-family homes, the addition of new residential developments does not mean that the state will run out of water, let alone be forced to choose between lawns and drinking.
Nonetheless, some are proposing restrictions on residential lawn use, such as regulating the amount or type of lawn a new residence can have, or requiring water conservation technologies to be placed in residential developments. These restrictions are not without precedent. The North Marin Water District limits new housing developments to 800 square feet of lawn, and requires new developments to have weather-based irrigation systems.
Weather-based irrigation controllers are a relatively expensive requirement, ranging anywhere from $150 to $2,500 for equipment and installation, and most systems also require annual subscriptions for data services and ongoing radio communication from the central data server to the local irrigation controller. These are the types of systems eligible for rebates, essentially subsidizing their expense with tax dollars.
Requiring this type of system not only adds expense for both homeowners and taxpayers, but also stifles newer, cheaper technology that is currently available but not widely known among irrigating homeowners because they are not promoted by rebates or regulations. This is a case where the biggest efficiencies are likely to come not from more regulation, but less.
Weather-based irrigation control systems are well-suited to large-scale operations like production agriculture. These systems monitor air temperature and rainfall, and use a system of equations and relationships to estimate evaporation and crop water use, or transpiration, the combination of which is commonly referred to as evapotranspiration, or ET. ET-based methods are well developed, but robust ET estimation requires a tremendous amount of ancillary information, such as soil type, vegetation parameters, wind speeds, relative humidity, and other information. Without these more complicated approaches, ET estimation is at best a general number rather than a precise measure of the water status of an individual location.
