How Does a Cistern Work?

Rochel Maday
Written by Rochel Maday
Updated November 2, 2021
The exterior of a house with a flower garden on a sunny days
Marje/E+ via Getty Images

A cistern is a system that collects and stores rainwater for household use

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When it comes to supplying your home with H2O, city and well water aren’t your only options. A cistern is another type of system that can keep water flowing to your home. But many homeowners aren’t familiar with cistern systems and how cisterns can help lower their water bill without adding much to their home maintenance routine. Learn what a cistern is, how it works, and what it can do for your home.

What Is a Cistern?

A cistern is a reservoir water system featuring a large tank made from either concrete, steel, wood, or fiberglass. It’s stored underground where it collects rainwater for household use and, in some cases, consumption. Cisterns range in capacity from 100 gallons to several thousand gallons. 

How Does a Cistern Work?

The mechanics of a cistern vary by system, but the main concept remains the same. The collection process usually starts on a rooftop where gravity pulls rainwater towards pipes leading to a cistern tank. Water passes through mesh screens to prevent large debris from entering the tank. 

The collected water is stored underground where temperature changes are less likely to be an issue. The water is also better protected from animals and insects. When it’s needed, water from a cistern is pumped by hand, drained by gravity, or pumped by an electric pump.

What Is a Cistern Used For?

Domestic Uses

The most common uses for cistern water are domestic, such as flushing toilets, cleaning laundry, and watering gardens. Cisterns are also commonly used on large rural properties like farms. They make it easier to keep fields watered and animals happy when the nearest hose hook-up is hundreds of feet away.

Consumption

Cistern water is typically considered non-potable. However, in some cases, water is collected in a cistern as drinking water (this is more likely on properties without access to city water). If this is the intent of a cistern system, the CDC recommends taking extra steps to ensure the water is safe to drink.

Benefits of a Cistern

Choosing a cistern as a main water source for your home can provide several benefits:

  • Cisterns save money. If you’re currently using city water, you can save on your monthly bill by using a cistern to provide some of your home’s water supply.

  • Cisterns manage stormwater. When water is collected in a cistern, peak runoff volumes are reduced. Less water enters the storm sewer system, which saves municipalities treatment costs.

  • Cisterns reduce pollution. Also related to reduced runoff volumes, cisterns prevent contaminants from entering streams that would otherwise receive rainwater. This means cleaner natural water sources with minimal erosion effects.

Cistern Maintenance and Water Quality

You should test the water in your cistern at least twice per year or whenever the water quality changes (e.g., color or odor). If tests show that your water is contaminated, you’ll need to find the source. Look for damage to the cistern itself. Tanks can crack over time. Also, check collars, lids, and screened vents for damage. 

If your cistern is damaged, consult a local plumbing professional on steps to fix it. Once you’ve identified the contamination source, repairs can be made. The cistern will then need to be drained, sanitized, and refilled. Again, this is often a job best left to the professionals.

Can You Safely Drink from a Cistern?

Water in a cistern can become contaminated, either from external sources or from bacterial growth while being stored. Heavy rains, storms, floods, pollution, and roofing debris can all contribute to contamination. This is why it’s important to know how to test and treat the water before consuming it.

What Is the Difference Between a Cistern and a Well?

Wells and cisterns both hold and provide water, but their collection process is different. While cisterns collect runoff rainwater, wells tap into supplies of groundwater like an underground stream or spring. Wells are dug into the ground and reinforced, whereas cisterns are often fully constructed and then placed underground.

Should I Install a Cistern?

A woman watering her vegetables in the garden
AzmanJaka/E+ via Getty Images

If you’ve purchased a home with a cistern, it’s worth looking into whether or not it’s operational. If so, it may be able to reduce your water cost.

But if your home doesn’t have a cistern, could it benefit from one? If you have the space, enough annual rainfall, the budget for an installation (installs can range from a couple hundred dollars to over $20,000 for large systems, according to HomeAdvisor), and an estimate of projected savings on your water bill, it’s a water source worth considering. 

Remember, you don’t have to use water from a cistern for everything. Using cistern water for your vegetable garden or washing machine can make a difference in your home’s monthly water usage cost.

It’s possible to install your own cistern, especially if it’s on the smaller side and used for light tasks. But when it comes to larger cisterns designed to hold enough water for a house, it’s better to reach out to the pros.

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