Why Flushing Hydrants and 'Wasting' Water Keeps You Safe

Flushing hydrants can be frustrating to residents in places with low water supplies, but it is essential to ensuring clean and safe water.
Interesting Engineering

You have probably seen it many times and thought to yourself, "what a waste of good clean water!" Flushing hydrants can be frustrating to residents in places with low water supplies or those who pay high premiums to keep their taps flowing. While it may seem like a waste of good clean water, flushing of hydrants is essential to keeping your water safe and maintain the integrity of a pipe network. Flushing hydrants can be done to not only test the fire flow capacity in the event of a fire, but also to remove sediment and rust from the water, or to maintain proper chlorine concentrations in your area.

First, let's look at flushing hydrants for the purpose of keeping chlorine concentrations high for disinfection purposes. Chlorine additions are common disinfection procedures in US water treatment plants, and it ensures that bacteria are not thriving in the water or pipe network. However, chlorine naturally degrades the longer it is in water, which means that water sitting in pipes for long periods of time or further out from the treatment plant can have concentrations lower than acceptable, creating danger. Hydrants are flushed to keep water moving and keep pipes from stagnating in this case.

Another reason hydrant flushing can be necessary is if water becomes stagnant in pipes, or water becomes contaminated. Sediments, rust, and even chemicals can sometimes leach into a water system from broken pipes or even the linings of the pipes themselves. Engineers recognize this risk and determine key locations where hydrant flushing will increase water quality.


The final reason hydrants may be flushed is to test or record flow values. Certain codes indicate the necessary fire flows from hydrants in order to maintain safety in the event of a disaster. Pressures and flow rates at hydrants can be drastically affected by other users' usage of water, or even possibly a burst pipe. Periodical testing ensures that there is enough water supply, which also can affect home and business owners' insurance rates.

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hydrant flushing[Image Source: Wikimedia]

To summarize, if you see a fire hydrant running for hours on end, it isn't the city just wasting water. If the city could keep the water, they would. After all, no one is paying for the water being flushed from a hydrant so ultimately the water utility loses some money. Now, you may say why not transport the water unsuitable for drinking to water a park or put it to good use? While this is a noble venture, it often proves much too costly, and dumping the excess down storm drains is the only viable solution. If you want to hear this directly from a water utility, check out the short video below about why Plano, Texas, a suburb of Dallas, often has to flush their hydrants.

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