Water pressure is influenced by a number of factors including ground elevation, distance from the treatment plant or pumping station, piping materials, and even water demand on any given day. Ground elevation influences water pressure because pressure is actually created by lifting water into the air above the point of use. This is why water is pumped up into water towers – to raise it above the point of use thereby creating pressure. As a result of the influence that elevation has on water pressure, higher elevations in a service area experience the lowest pressures and lower elevations experience the highest pressures. Ground elevations in Des Moines range from 800 feet above sea level on the east side of the City near the Des Moines River to more than 970 feet above sea level in northwestern areas of the city. This 170 feet of elevation difference represents a water pressure variation of 75 pounds per square inch (psi). The distance from the pumping station and changes in water demand introduce additional pressure variation resulting in the potential for significant pressure differences across the city. Des Moines Water Works (DMWW) manages water pressure using pressure zones, water towers and booster pumping stations, like the new booster station near the Des Moines Airport.
The City of Des Moines is divided into four pressure zones. Each pressure zone has dedicated pumping stations that pump water into the zone to maintain pressure. Water towers help stabilize pressure in some zones. Water flows into the towers during hours of the day when there is less water demand and flows back out to satisfy higher demands. The combination of water from the pumping station and water flowing out of the water tower acts to stabilize pressures in the zone.
Water pressure in the Des Moines system averages 50 psi but ranges from 35 psi to more than 100 psi depending on the location in the city. Thirty five psi is Water Works Board established minimum system pressure in Des Moines. Plumbing code requires that residential properties in areas with water pressure in excess of 80 psi be protected by pressure regulators installed on the water service lines.
Older, smaller diameter service lines or corroded service line components such as valves or couplings can cause low pressure for some customers. Currently, DMWW Rules and Regulations require that new residential service lines be installed using one-inch diameter copper or cross-linked polyethylene (PEX) pipe. Historically, ¾-inch or even ½-inch pipe was used and in some cases the pipe was galvanized steel which is subject to corrosion when buried. Homes with smaller diameter service lines, especially those with ½-inch galvanized pipe service lines, may experience low pressure due to restrictions in the pipe. Galvanized steel pipe inside the home may also contribute to pressure problems as corrosion occurs on the inside of the pipes.
Customers who feel they may have pressure problems can visit with a customer service representative for more information by calling (515) 283-8700.