Peak Demand Dictates How Cities Build Water Infrastructure

It's no surprise that demand for water in the Phoenix Metro area reaches its peak during the summer months. What may be surprising is that demand nearly doubles from the winter months to the summer months. In February 2015, City of Peoria customers - businesses, apartment buildings and homes - used 2,940 acre-feet of water. In July, Peoria’s peak rose to 6,516 acre-feet of water. (One acre-foot of water is enough to cover an acre to the depth of one foot or enough to serve an average of three Arizona households for a year.) In December 2015, City of Mesa water customers used 5,899 acre-feet of water. In July 2015, Mesa water customers used 10,503 acre-feet.

The annual pattern of peak demand can look slightly different from year to year, depending on fluctuations in heat and when monsoon storms arrive. The chart below shows Mesa’s annual water production for the past 5 years. Peaking in Mesa happens most often in July, but a hot June and a good July monsoon can mean that the peak month could be June.

Watching water-use trends and peak demand is critical to planning and building water infrastructure. Here’s why:

•  Annual Peak Demand: Cities build infrastructure to meet annual peak demand. It would be cheaper to order just enough water and build just enough pipes, pumps and small reservoirs within a water system to meet average water use but that would make water delivery to your faucets unreliable during peak demand times. More is invested in water treatment and distribution systems to ensure they are built to provide water for the hottest days when landscape irrigation systems, pools and cooling towers are working at maximum capacity.
• Daily Peak Demand: Each day, demand for water peaks in the morning and, again, in the evening hours. That means water managers are diligently filling a water system’s reservoirs overnight to make sure enough water is ready to be pumped to homes when hundreds of thousands of residents step into their showers between 6 a.m. and 7 a.m. Then water managers dial back around 9 a.m. when demand lessens and to prepare for the after work demand.

Small reservoirs keep water available for peak demand. Photo: City of Mesa

• Safety Peak Demand: Being ready for daily and seasonal water demands isn’t enough. Water managers must maintain water supplies and build water systems for the what-ifs. What if it’s 6 a.m. on a July morning and firefighters call for more water to fight two house fires and a brush fire? What if the system is just dialing back to accommodate a low demand time when a water main breaks spewing hundreds of thousands of gallons of water meant for customers into the street instead? A water distribution system must have supplies, pipes, reservoirs and pumps in reserve to keep water running to customer faucets while employees fix the break or provide water for fire suppression.

Most cities, including Mesa and Peoria, use a computer program called Supervisory Control and Data Acquisition or SCADA to track water demand throughout their systems. The program allows city employees to keep their eyes on each part of the water distribution system remotely and in real time. Operators use this innovative computer program to review water distribution continually throughout their service area and to track peaks in demands. For example, a sudden change in pressure could mean firefighters need high volume and increased pressure to put out a fire, a construction site is filling a large water tank, a reservoir is overflowing or there is a break in the system and the city is losing water.  Utility workers can quickly respond to investigate and correct the problem to significantly reduce any disruption to your water service. 

During the last two decades, while Mesa and Peoria have grown by hundreds of thousands of people, the water used by city customers, even during peak demand months, has remained nearly flat. Cities helped to fuel this accomplishment by promoting a conservation culture, which includes encouraging drought-tolerant landscapes and the use of water-efficient appliances and fixtures, and helping residents find and fix leaks. Want to help lower your city’s peak demand? Start outside where as much as 70 percent of a home’s water is used. AMWUA’s Smart Home Water Guide can help you find and fix leaks. AMWUA’s landscape pages can help you select drought-tolerant plants and trees, design a lovely yard, and efficiently water your landscape for maximum beauty.

For 47 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit www.amwua.org .