This winter residents of El Paso, Texas experienced unusually cold weather. Temperatures reached six degrees Fahrenheit in early February, the lowest recorded for the city in 120 years. In short order, El Paso became a city of frozen and burst water pipes where businesses and daily activities were seriously disrupted. Faced with a significant water shortage, El Paso Mayor John Cook declared a water emergency and residents were placed on mandatory 24 hour water restrictions that lasted for several days.
El Pasoans were asked not to shower, wash cars, use dishwashers, or anything else that might use large amounts of water, according to the El Paso Times. Water restrictions closed schools and impacted local businesses, including restaurants, laundromats and car washes. People in homes experiencing water outages or leaks were advised by utility officials to boil water before drinking it in the event supplies had become contaminated through pipe breakages.
You may recall from high school physics that water is one of the few substances in nature that expands upon freezing. (That is why ice cubes float and you can skate on a frozen lake while fish swim below.) Water and ice are essentially incompressible at the yield strength of metal and plastic pipe. So, as the temperature plummeted in El Paso, water pipes burst, flooding homes and businesses.
Why El Paso? Every winter we see heavy snow and sub-freezing temperatures in the northern parts of the country in places such as Michigan, North Dakota and Massachusetts, and yet, we don’t hear of widespread water infrastructure damage. One reason is the regional difference in urban planning. Water mains in North Dakota must be buried at a minimum depth of eight feet to avoid freezing. In contrast, in warmer regions like El Paso, pipes may be buried at very shallow depths of no more than a few feet because protection from freezing is not a routine concern. But it was not a “routine” winter in El Paso: One break in a shallow water main caused a spill of 0.5 million gallons overnight, virtually draining water storage tanks and creating the serious water shortage.
One insidious scenario is that freezing may cause small cracks in water mains from which leakage is sufficiently low that it is not detected on the ground surface. Such small cracks pose a problem with back siphonage of contaminated ground water into the water distribution system during periods when the mains are not pressurized, such as during repairs. This scenario underscores the importance of maintaining and monitoring a residual level of chlorine disinfectant throughout the water system. Any noticeable drop in the chlorine residual is a warning of possible contamination that bears investigating.
Events this winter in El Paso are a reminder that urban infrastructure throughout the US is in need of modernization and upgrading. As part of the necessary improvements, city planners should consider shoring up water delivery networks against greater extremes of weather. It’s more than about losing water for a few days: it gets to water quality.
For information on what you can do to prevent water pipes in your home from freezing, or how to thaw frozen pipes visit the American Red Cross website.
Jerod M. Loeb, Ph.D. is Executive Vice President, Healthcare Quality Evaluation at The Joint Commission in Oakbrook Terrace, Illinois.