Frequent Question About Pumps vs Tanks
We get a frequent question about the tank project questioning if replacing the tanks is better than using pumps spread around the town, or some other pump design. We're not engineers, or experts in the details found during the 4 year course of the project, so we went looking in the water tank project website and found this explanation in their Frequently Asked Questions section of the website. There is a ton of information about the project at their project website at:
https://www.westonma.gov/1828/Water-Tank-Replacement-Project
There are links to the video recordings of all the Select Board Water Tank Working Group meetings if you are a glutton for punishment, or if you think you might vote against the project. At least know the details of the project and respect the very hard work of all the Select Board members and learn about their deliberations before you vote.
All 3 Select Board members worked extremely hard above and beyond their normal heavy work loads to dig into the project elements in an admirably collaborative and productive way. Especially in last week's meeting they went through every possible issue that has been brought up and discussed each topic and indicated where they stood on each issue.
FAQ sites can be found both on the front page of the project site at:
https://www.westonma.gov/Faq.aspx?TID=57
This their description of the pumps vs tanks question. taken from the town's water tank project website.
Can Weston Fix its Water System with Pumps?
A question that has come up with some regularity over the years that the Town has been discussing Weston’s water insufficiency is whether the problem can be solved with pumps rather than by raising the height of the water tanks. In some ways, it would be an appealing solution. While we would still need to build new tanks, since the old ones have reached the end of their useful lives, we wouldn’t have to build tanks that are proposed to be 40 feet taller than our current tanks. (Because the old tanks need to remain in service while the news ones are being built, the issues of finding sites for those tanks, and the need for a land swap, don’t go away.) Pumps are not the answer. They are more expensive and less reliable. Furthermore, they would not meet state requirements for fire safety. Website link:
https://www.westonma.gov/Faq.aspx?TID=57
From Jan 2023 FAQ’s, located by scrolling to the very bottom of the westonwatertanks.com page.
FAQ # 5. Can we solve our water provision issues using more pumps or using the pumps we have more continuously?
We cannot solve our water issue by relying on pumps. It is true that in very small water systems consisting exclusively of residential customers, pumps can be sized to provide peak-hour demand and firefighting volume. In fact, that is exactly how our small Black Oak pump station is designed to work. But this station only serves a very small population. In large systems, meeting peak-hour demand 1 and firefighting volume would require prohibitively large and expensive pumps.
Under standard water engineering practice, pumps are designed to meet the maximum-day demand, 2 and tank water storage is designed to supply the peak-hour demand above the capacity of the pumps. To instead design a system that relies on pumps to meet the peak-hour demand would be complex, requiring more pumps to supply a greater range of flows. Not only would we need more pumps, but the pumps would need to be more powerful. Furthermore, system piping would need to be significantly upsized, all of the electrical systems in the pump station would need to be increased, the capacity of the emergency generator woul need to be increased, and the control systems for the additional pumps would need to be upgraded. Using pumps rather than tank storage to meet peak-hour demand would be more complicated and less reliable than using water tanks with adequate storage capacity.
Furthermore, the Insurance Services Office, which sets the Town’s insurance rates, does not consider reliance on pumps alone to be a suitable or reliable provider of water for large fire flows. The State also requires that water needed for firefighting come from water storage. Engineering practice and state guidance both dictate that pumps be designed to meet only the maximum-day demand. Water demands that are higher than that, such as peak-hour demand, should come from water storage. Our pumps were designed so that one pump meets average- day demand, and two pumps meet maximum-day demands. The third pump is a backup pump.
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Peak-hour demand is the maximum demand that occurs over a one-hour period. Peak-hour demand is the maximum volume that must be provided by all sources in the system (water supply and storage).
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Maximum-day demand is the maximum day of water use that occurs in a given year.
Besides being the economical way to provide water pressure, storage from a water tank of adequate size and elevation harnesses the power of gravity, which is much more reliable than electric pumps. Gravity works even when the power goes out. That is why tanks of adequate size and height are the standard, tried and true approach to the provision of municipal water. As climate change increases our need for resilient systems in the face of ever-fiercer storms, a water system based on the power of gravity rather than the electrical grid is by far the wiser approach.
(Average day demand is defined as the total water use in a year divided by 365 days)
Hope this information is helpful to you.
Sincerely,
Alan Day