Anyone here know much about cisterns? About all I have is a general impression that people now consider them dangerous (?) and those who have old ones try to fill them in.

It's pouring down rain today here where I live, and I'm looking at the house across the way shooting umpteen gallons a minute out the end of the downspout - which runs off down the gutter, then storm drain. I'm thinking, what a waste.

We've had a couple of summers of drought in a row here, and what we could have done with all that water then. It just seems to me that for those with the room for one, that saved water could be very useful for watering the garden, washing clothes, flushing toilets and - with purification - drinking and cooking, when there might be a need.

Is there an overflow drain on those things so the water can run off and be refreshed? Or do they end up nasty and omeba-infested,like some neglected swimming pools I've seen?

I don't know about cisterns, but rain barrels at the end of the down-spouts are a great way to keep toilet flushing water handy.

I might hesitate to drink the water without purifying it first...

I'm baffled by this. I mean anything can be dangerous. What specifically is considered the danger with cisterns?

Regarding an overflow, it just depends on your system. Some cisterns have an overflow, and some just fill until full and then anything more will just run off.

As for a cistern becoming contaminated by bacteria and so on it will depend on how well you take care of it, just like a pool. However, pools are much harder to take care of due to the generally large surface area and because they're open to the environment.

Rainwater is a relatively clean source of water, depending of course on your location so most of the initial worries will come from the contaminants it encounters on the way to the cistern. For example, if you have a lot of pigeons on your rooftop, whatever they leave behind is going to be washed into the cistern.

Other types of contaminants and debris such as leaves, twigs, pollen, mold spores and so on can be avoided by diverting the first rains away from the cistern and then using screens and simple inlet filters. Still, something is bound to get through.

A secondary concern for contamination will be contamination of the cistern itself. You'll want it to be covered to prevent animals from drinking out of it, defecating and urinating into it, or falling into it and dying. You'll also want it covered well enough to prevent mosquitos from laying eggs in the stored water.

The above should be sufficient for water to be used in just about everything except bathing and consumption.

In the end you'll want a good filter if you're planning to use the water for consumption in the case of an emergency. And as always, chemical treatment or boiling will help as well.

I'm really starting to like some of the UV water treatment elements out there that can be sunk into cisterns and that run on small solar panels.

This is just a few things I've learned about while studying the subject. I could have missed something. If so, please let me know.

Just Google it..tons of info..State of Florida has a big page with the math to find out big you need to make it per square foot of catchment..having said that we are a Watershead Friendly Household.at least thats what the sign in our rain garden says..the city of Minneapolis will help pay for the plants to go into a rain garden.those are plants that can be flooded and sit in water untill the rain soaks in.water from the downspots runs in and pools and gets back into the groundwater supply rather that running off the streets and into the river..our rain barrel collects water that we save for watering in door plants during our long winters.

I don't have a proper cistern, but I do collect rainwater in several large above-ground tanks for watering parts of our garden.

The water does go a bit funky after a while. It's impossible to keep some bio debris from getting in, and algae will grow if there's any light at all.

If I had a very large tank, especially underground, I would add aeration to keep it relatively fresh. Otherwise it will smell sewer-ish. I'll bet that even an aquarium pump would do wonders.

BTW, the good part about an above-ground tank is that you can gravity-drain the water to where you need it. An underground cistern would require a pump and the juice to run it.

I had to fill a couple in and did the concrete formwork to pour one new one.
They are really just a big water tank.
Yes the water can go stale but they are covered and usually stay pretty clear.
Overflow? Well newer ones normally have a provision for an overflow to some kind of drain or spillway.
Usually there is no provision to simply open a valve and drain them. You would likely pump them out with a sump pump or by bailing.

When cisterns were common people did not really know about water born diseases and the cisterns tended to be about as safe as their shallow, run off contaminated, hand dug wells were.
There is no algae if there is no sunlight, no algae means there is not much for bacteria or other microbes to feed on, unless a mouse falls into it.
Most pathogens sink in still water too, so water pulled from the top of the cistern with a bucket was likely cleaner than the well water they had then.
A lot of our grandparents died from wells contaminated by runoff every spring. That was what they called spring fever.

When rural electrification (beginning in 1936) made electric pumps available, and the ability to drive deep wells that were cased to prevent the water from the barnyard running into them every spring cisterns went out of fashion.

Today the biggest danger from old cisterns is that somebody might fall in.
The covers do get weak over time.
Old wells are dangerous the same way.

I only ever saw the one new cistern and it seemed like an expensive way to store water.
I have seen people bury the plastic Intermediate Bulk Carrier tanks for water storage, but the only real reason they buried them was to hide them from sight.

IBC tanks

The two stacked tanks in this picture are 220 gallons each.
I know they are available up to 550 gallons but they are not cheap.
A new 550 gallon tank with fittings would likely cost close to $3,000 and a recycled one would likely be between $1,000 and $1,500 to buy.

These have taps near the bottoms.

45 gallon drums are easier to handle and much cheaper to get.

I suppose you could chemically treat the water to keep it fresh with something like sodium bisulfite, but I don't know enough about water treatment to talk about it, and I would still want to boil it.

Cisterns were driven out of popular use in the south because the open ones tended to help provide a breeding ground for mosquitoes. It caused some nasty diseases a long time ago. In some areas they were outlawed. In our area a number of folks that are not on city/county water have underground cisterns instead of wells. I guess it is cheaper to build a cistern here instead of drilling a well. Every time I have to dig a hole I wonder how far I will get before I hit a piece of rock. Record so far is 18". Usually I hit a rock (usually large flat ones) as soon as I push the shovel into the ground.

In my former farmhouse in Iowa, I had an old cistern attached via piping directly to the house. The house also had a concrete underground chamber with a large metal tank with a water drip mechanism at the top. Calcium carbide was placed into the tank and, when dampened, the resulting acetylene gas was piped into the gas light fixtures in the house. Unfortunately, essentially all the gas fixtures had been removed. The cistern had been capped years before I acquired the place, but I removed the cap and installed a hand-operated pump which worked great for pumping up water for non-drinking use. In the course of uncapping the cistern, I inspected it carefully (it was about half full of water presumably just from seepage from small cracks) and saw the skeleton of a snake in the bottom. Since I wasn't using the water for drinking, that wasn't of great concern to me. Originally, the cistern was filled by run-off from the farmhouse roof. I wish I still had that house, but sold it before moving to the west coast.

When I went to Portugal this last trip, 99% of there water was from Cisterns. The water from the Cistern was clear and I treated it with a steripen every time I drank out of it, we joked about a fish was living in it but other than that it's been there for over 30 years of hard use everyday and supplies most of the water for everything from washing cloths, drinking, bath,etc.. I'm a firm believer of them and I would definitely build one above ground and enclosed for ease of maintenance with filters and solar UV as was suggested by Nicodemus. They are a great source of off the grid dependable water that taste great, just rough filter it and UV treat it and everything would be fine.


Water is tapped off the roof and delivered in this above ground enclosed concrete cistern and is almost always full all year. They said it is really rare it drys up but they live on a island that rains all the time. Over 30 years of hard use 24/7.

Just google 'rainwater harvesting' and you'll get lots of info, esp from Texas.

Falling on a clean surface, rainwater is twenty time cleaner than the cleanest ground source of water, anywhere.

If you have acid rain, hang a bag of limestone chips in the tank to add a bit of alkalinity.

Plastic tanks are the cheapest, but the most susceptible to UV damage over the years. But if you wrap the tank with a couple layers of chicken wire and apply an inch or so of concrete to it, it will both protect the tank (practically forever) and keep the water cooler. I understand that the moss-like algae growing on the walls of the tank are beneficial to the water.

Two good books on harvesting rainwater:

Water Storage: Tanks, Cisterns, Aquifers and Ponds by Art Ludwig (the Greywater Oasis guy).

Rainwater Harvesting for Drylands and Beyond (3 vols, 2 are out now) by Brad Lancaster.

Sue