Thanks to pines of rome for posting a thought-provoking comment regarding different pipe types susceptibility to freezing and bursting on Rule of Claw’s diary yesterday. This led to a good conversation about municipal water infrastructure in this country. Since advising municipal water and wastewater utilities on pipe type is my profession, and there seemed to be the desire for more info on this topic, I put together what wound up being a pretty lengthy diary of my own.
Today, many Texans are living through a massive failure of their municipal water infrastructure brought on by a massive failure in their electrical infrastructure caused by a massive failure in public policy and what people in many parts of the country would consider a minor winter storm. Is this combination of ineptitude and unusual weather unique to Texas today? How robust are municipal water systems in the rest of the country?
Water system health is obfuscated and hidden in rarely viewed reports or buried in the fine print of billing statements. Furthermore, when it comes to transmission and distribution, the vast majority of our water infrastructure is underground: out of sight, out of mind. We drive over potholes in our roadways and see rusted girders supporting aging bridges and overpasses, but as long as water is coming out of the tap, and no one has told us it is unsafe to drink, our water infrastructure seems to be functioning just fine. But if water is your livelihood, you have no choice but to understand the dirty details of municipal water system vitality.
Three key metrics define a city’s water system health: water main breaks, water loss rate, and cycle time.
The most basic metric is water main breaks. This figure is meaningful because aging infrastructure is more prone to main breaks; aging cast and ductile iron develop weak points due to corrosion, while aging PVC is more susceptible to rapid crack propagation (RCP) and separation at the joint. Main breaks expressed either as breaks per mile or breaks per capita tell the same story: more is worse.
Water mains are breaking right now in Texas due to cold temperatures as pipes are buried at relatively shallow depths in that part of the country. Pipes that have never been exposed to ground freeze are currently experiencing such conditions. Generally, water mains are buried below the “frost line” or the anticipated depth of ground freeze for any particular location. This both prevents water inside the pipe from freezing, as well as protects bell and spigot systems from the ground movement associated with freeze-thaw cycles, which can cause the unrestrained joints of ductile iron and PVC to separate.
Mains can also break due to surges in pressure. For most pipe types, repeated surges caused by pumps turning on and off or simple pressure variances lead to failure by what is known as “cyclical fatigue”: the pipe material is not ductile at normal operating temperatures and thus cannot swell to accommodate pressure increases. While a PVC or metalic pipeline may not immediately fail upon the first surge or even the thousandth, it will become weaker with every cycle until the pipe wall eventually yields under a sudden increase in pressure.
Water loss rate, commonly referred to as “non-revenue water” (yes, municipal water is stolen through unmetered taps), is the difference between the quantity of water that leaves treatment plants for circulation and the amount that is measured by metering at (almost) every end user. According to the EPA, the national average water loss rate is 16%. There are outliers like Niagara, NY or Missoula, MT which lose close to 50% of the water that leaves their treatment plants, water that citizens are paying for to be sourced, treated, and pumped is simply lost into the ground through leaks in failing pipelines.
Leakage is not a problem unique to aging infrastructure. Bell and spigot systems have an allowable leakage rate that can be calculated based on the pipe diameter and length for the DAY THE BRAND-NEW PIPE GOES INTO SERVICE. According to the AWWA (American Water Works Association) PVC Design and Installation Guide M23, the allowable leakage rate for new PVC is 10.5 gallons per day, per mile, per inch of pipe diameter. That means 10 miles of brand new 12” PVC is permitted to leak 459,900 gallons of water every year. This is why most Western European nations do not permit PVC to be installed for potable water. Nor do Phoenix, Calgary, or Miami.
Most states legally require municipal water systems and private water utilities to track and publish their water loss rates, though unless a utility is losing significantly less than the 16% national average, that figure will be difficult to find. Perhaps it is in the fine print on your bill, along with warnings about water quality hazards. Give it a read someday. You may find that you are “potentially” being exposed to asbestos, lead, or radiological contamination every time you take a sip.
Water loss carries the obvious stigma of poor resource management. In the desert Southwest, where water is scarce and frequently sourced hundreds of miles from city centers, this is an obvious tragedy. In other regions, water is abundant and not considered as valuable. Water loss also carries a financial consequence, both in the loss of a purchased, treated resource, and in a significant energy cost. In most cities, the biggest electricity user is the water utility whose pumps run constantly, sucking water out of aquifers and pushing it through mile after mile of main and service until it reaches a faucet on the top floor of the tallest building in town.
Finally cycle time tells the full story of municipal (mis)management better than the other two metrics. The referenced “cycle” represents a full replacement of every foot of water main within a utility’s boundaries. It is calculated by dividing the miles of water main in service by a 5-10 year average of miles of main replaced annually. Rarely is this figure published, but the numbers needed to calculate it are often readily available, or at least accessible through FOI requests. Cycle times under 100 years are generally considered healthy regardless of whether or not a utility’s chosen pipe type can boast an expected service life of over 100 years.
As one might guess, affluent communities tend to have lower cycle times. Bozeman, MT is a hardcore ductile iron town and can claim a cycle time below 100 years (as well as low main breaks and a water loss rate well below the national average). Their system is robust and healthy because they can pay to keep it that way. The same is true for Madison, WI (93 years) and Palo Alto, CA (98 years). On the other end of the spectrum is what many in the business refer to as the “500 Year Club.” Cleveland, Minneapolis, and Charlotte are just three of the many American cities who can claim membership. There is also a “700 Year Club” whose members include, but are certainly not limited to Honolulu, Fresno, and Raleigh.
Each of these metrics alone provide a snapshot of system health, but viewed in concert provide greater insight to the big picture of municipal water system management. Let’s start with main breaks and see how the other two metrics tie in: cities repair main breaks using money from their water system’s operations budget. Repairing water main breaks is expensive even though repairing the pipe is often a straightforward task of securing a repair clamp onto the damaged section of pipe. Excavation can be extensive and clean-up costs are widely variable depending on how much water flowed to the surface and the amount of property damage that water inflicted. The more water main breaks a utility has to repair in a given year, the greater the chance they exceed the budget allotted for repairs in their operations budget. So how do they cover their repair costs? By taking money from their capital fund. When they rob the capital fund, they limit their ability to conduct pipeline replacement, increasing their cycle time. As their infrastructure ages, the chance for main breaks increases and more money is pulled from capital to conduct repairs. As the cycle time increases, aging water mains develop more leaks and water loss rate increases. It is a vicious cycle and one that far too many cities in this country are stuck in, slowly spinning out of control, unable to replace old, even dangerous infrastructure. Many cities East of the Mississippi still have wood pipe in service. Wood. Wood water pipe. New wood pipe hasn’t been installed since the late 1800’s. Do you think that pipe leaks? Do you think 120 year old wood pipe harbors biological growth?
…but we’ll go deeper into materials in part 3. For now, check out Part Two!