Challenging Assumptions – Water Demand and Population Growth


Our new Money Pit report makes the argument that Southeastern communities don’t need to turn immediately to building new reservoirs in order to secure their future water supply – instead, new reservoirs should be the last option on the list. The report shows how we can find new water supply through lower-risk practices like water efficiency, ratcheting water demand downward rather than building larger and larger storage infrastructure.

Admittedly, the idea of water demand going down in the future can be a tough sell in any community (like many here in the Sunbelt) looking to grow in the years and decades ahead. But here’s an important truth: growing population does not necessarily equate to growth in water demand.

Communities across the country have demonstrated that it is possible to reduce overall water consumption while population grows. Check out the chart here:

In Seattle, total water consumption has declined by 30 percent since 1990 – down to levels used in the late 1950s – while population has increased 15 percent during the same period of time.

Meanwhile, Raleigh, North Carolina’s service population grew by 30,000 customers between 2007 and 2011, at the same time that the city reduced demand by 2 percent.

And water systems that are part of the South Florida Water Management District used far less water in 2010 than in 2000 – a difference of more than 80 million gallons per day – while population grew by 620,000 people over the same period.

The lesson here is that water demand projections need a very hard look before we let the numbers justify major public spending in an attempt to store water that may not even be needed in the future. Take a look at the second chart here: Officials in Seattle, Washington have conducted 11 water demand forecasts since 1967, and actual demand has never in the past approached the forecast amount. The take-home is that water ratepayers and local taxpayers end up paying for water storage infrastructure that’s unnecessary at the end of the day.

The prudent path for water supply planning, then, is to incorporate aggressive water efficiency plans into demand projections before determining future needs. Not only can this reduce capital costs for any capacity expansions, or push expansions further into the future, it also helps a water system avoid spending for capacity that it doesn’t need – for water that its customers don’t need, and for which they shouldn’t have to pay. In this way the water utility avoids paying today for water it may not need for another 40 years, if at all.