Saving Water and Building Our Economy
December 1, 2021
Professor and Head
Hydrology and Atmospheric Sciences
University of Arizona
Room 122 JW Harshbarger Bldg. #11
Tucson, AZ 85721
Water is the most important resource when you live in the desert as we all do. In the coming decades we need to embrace the history of Arizona where we have solved our water challenges collectively and ingeniously. We have long known that we have allocated more water rights to water from the Colorado than there is water in the river on a long-term basis and now this has led to the situation today where water deliveries to Arizona are being cut. These cutbacks are occurring as climate change is making our world warmer which through reduced snowfalls, longer growing seasons, and increased plant water demand is squeezing water users by increasing water demand and decreasing supply.
Fortunately, we have a long history of coming together and working to solve our water problems here in Arizona. From the creation of the Salt River Project, to the century long campaign to build the Central Arizona project the people and leaders of Arizona have worked together to solve our water challenges. These efforts have extended into individual and collective efforts to conserve our water resources. Total water withdrawals from the environment today in Arizona are less than they were in the 1980’s and about the same as in the 1950’s.
Water usage didn’t change overnight. While lawns were common across the state in the 1970’s today they are less so. The reasons for the decline involve increased costs and the embrace of xeriscaping. Similarly declines in water usage inside residence and commercial facilities benefited from improved technology in low flow appliances and plumbing fixtures and conservation incentives from utilities. Bigger structural changes have happened as well. Today we treat effluent to higher standards and reuse a large fraction of it on communal irrigation spaces like school grounds and parks. Still, we have much to do in matching the water available to the right specific use.
While we have come far in reducing water usage there is more that can be done. In the early 1970’s per capita water usage in Tucson, AZ was over 200 gallons per person per day today it’s below 100. It might seem we have done what we can but in Australia per capita water use in the residential sector stands at roughly 40 gallons per person per day. I suspect water usage in the residential sector will continue to fall by 1 to 2% per capita per year as it has in the past several decades. These declines are likely to come from the traditional plumbing fixture, appliance, and landscape changes we have seen in the past. These strategies are not likely to be enough to meet the declines in water from climate change, the increased demand from hotter temperatures, and the distance we still are from sustainable water use.
To meet these demands we need to look to non-traditional water sources. One of these sources is sewage or effluent water which can be utilized either on site through greywater re-use. Household effluent is divided between human and kitchen wastewater – which is called black water and needs to be treated to a high level to minimize risk to human health while grey water (e.g. shower, washing machine) water can be reused on landscapes with little risk. Many newly constructed houses now have grey water stub outs and are plumbed to enable the diversion of grey water separate from blackwater on site. In addition to this on site use we should expect utilities to continue to reuse effluent for landscape purposes, recharge, and direct reuse once suitable treatment of these waters has been completed.
In the outdoors we need to emphasize the use of a different alternative water source – rainwater. We have often thought of this water source as a hazard to be eliminated – sent to our washes and away. But putting rainwater to use to meet our water resource demands is a key next step to minimizing or even eliminating the use of potable water resources for our landscapes. The winter and summer rainy seasons in our desert make capturing and using these waters valuable. There are two ways for us to capture this resource active and passive methods. Active methods include rain barrels and cisterns. These systems often store water from roofs and store it above or below ground. These storage systems are expensive, typically about $1-2 per gallon of water that can be stored. While expensive these systems pay dividends over decades and give users control over when and where their landscape is irrigated.
Passive methods diverting water from roofs, parking lots, driveways and other hard landscapes into basins surrounding plants. These methods are low cost and easy to implement. These methods put water where we need, it in the ground at the roots of plants/ The soil beneath our feet also represents a huge storage volume capable of storing 1000’s of gallons. Passive water harvesting systems are used broadly already with communities requiring these sorts of practices in commercial settings and incentivizing active and passive water harvesting.
The water challenges we face in Arizona are real but we have solved our problems before and can do so again. Greater efficiency and conservation are one arrow in our quiver but not the only ones. And we can find new water sources inside of our communities like effluent and rainwater.