How to determine the value of an intermittent water system

More than a billion people worldwide depend on intermittent water systems that turn and off depending on use, need, and the available supply. In some cases, the pipes can be empty for most of the week and only turned on for a few hours. 

There are many benefits to this kind of system, including water conservation when there are shortages. Having empty pipes also prevents leaking. 

But intermittent systems can be problematic and increase the risk of contamination as well as leaving people without water when they need it most.

David Taylor, a professor of engineering at the University of Toronto, has developed a new framework to assess the benefits and challenges of an intermittent water system by factoring in hours of operation, demand, water sources, and damage. 

Having a unified framework that focuses on demand and supply rather than the complexities of the system’s inner workings helps explain why the systems are in use and how an intermittent system can help meet the United Nations Sustainable Development Goals. 

Taylor worked with water companies in Delhi to see how intermittent systems meet demand. Working with a detailed hydraulic model of the water systems in Delhi, Taylor quickly realized that these models fall short. 

“These systems are chaotic,” said Taylor. “There are often pipes or valves that are missing from the official charts. We usually don’t know as much as we think we do, and in that situation, fancy models can’t tell us much.”

Rather than focusing on the nuts and bolts, or pipes, in this case, Taylor tried a different approach and created a model under the assumption that he knew nothing about the network. 

The result was a single equation model that links consumer demand and need and shows how system changes impact customer satisfaction. If customer demand is not met, for example, an intermittent system may double its supply time. 

What’s unique about Taylor’s framework is that it shifts perspective from asking how much water is saved or wasted, to how meeting demand or changing supply times increases the risk of leaks or contamination. 

“The model lets you see right away what the effect of altering a parameter is going to be, whether it’s leakage or demand or whatever,” said Taylor. “That enables you to do these back-of-the-envelope calculations and determine whether what you’re proposing is feasible.

The new model could be used to compare and improve existing intermittent systems or create new ones. 

Taylor outlined his model in a paper published in the journal Water Resources Research. 

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By Kay Vandette, Earth.com Staff Writer 

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