Why would you want a garden cistern?
- You, or your garden, have outgrown your rain barrel.
- You want plants that need irrigation, and you don’t want to pay that water bill.
- You want to use rainwater to irrigate rather than chlorine-treated drinking water.
- You want to reduce the amount of stormwater running off your property, perhaps because of flooding concerns or combined sewer overflows.
Garden cisterns are distinct from cisterns for drinking water use. At its most basic, a garden cistern is similar to a larger rain barrel. It catches water that runs off a roof when it rains and stores that water for later use. As climate change continues to weird our weather, more people have a need for landscapes that withstand drought and heat. Sustainable stormwater management like garden cisterns can be a smart addition to such a landscape. As I’m reading up on sustainable home components for my next house, I’ve made these notes on cisterns:
Cisterns for non-potable garden use are much simpler than those for drinking water, and therefore less expensive. Larger ones may be underground, but smaller ones often are cylinders, like a cross between a small grain bin and a large rain barrel with a roof. People also make DIY garden cisterns from repurposed tanks or pools. Garden cisterns capture rainwater off the roof and screen it to keep out leaves and debris like a rain barrel, but cisterns are generally light-tight, which keeps algae from growing. They may be less maintenance than rain barrels and last longer because of that. Galvanized steel with a plastic liner is a common material choice, although there are others.
Site: You want to put your cistern next to the roof where you catch water but uphill from where you want to use the water. This lets you simply attach a hose to the spigot to get water to the garden. If that’s not possible or the cistern is underground, you need a pump, which adds cost and upkeep. You could alternatively plumb an underground water line to the garden, which will eliminate fussing with hoses but also cost more.
An area of ground 15’x15’ should be plenty of room to fit a cistern in.
Cost: Per gallon of water stored, purchased cisterns are generally less expensive than purchased rain barrels, with DIY rain barrels and DIY cisterns both being far less expensive. Because of the weight of water, cisterns need a solid surface to sit on, like a concrete pad. Including that concrete, an 800 gal aboveground garden cistern might cost you $1000-$2000 in Connecticut at this writing, depending on how much work you hire someone to do and how fancy it is.
Cautions: do everything you can to keep wildlife and children (!) out of the cistern- any access into where the water is should be locked.
Don’t underestimate the weight of 800+ gallons of water – be sure your container is sturdy enough to hold it, well supported, and not on a slope where it could tip over.
Roof runoff can be really dirty – do not even think about drinking the water without doing real filtration and treatment on it!
Cisterns are large, but they can look good with careful design and planning and good material choices.
This link has some pretty pictures of professionally designed cisterns at homes: https://www.houzz.com/magazine/is-a-rainwater-cistern-right-for-you-stsetivw-vs~54846303
Reliable information about drinking water cisterns that also has good tables about calculating runoff from building size: https://extension.psu.edu/rainwater-cisterns-design-construction-and-treatment
**Disclaimer: This blog post is for informational purposes only. Hire a licensed landscape architect or engineer to ensure your cistern is designed and constructed safely.