Suburban rainwater tanks

Suburban rainwater tanks asks what volume you would need to plan for your home and garden, and gives thoughts on an underground reservoir, rather than plastic or fibre-glass storage chambers.

We have both systems; each has its merits. Having done it piecemeal my conviction is to do your planning first, and then build a big enough reservoir that will store sufficient water for a drought. Raising the wall is complex; better to do it right the first time.

This page was last updated by Bernard Preston on 21st February, 2020.

A fibreglass water tank is the best above ground storage chamber, but how many of these do you need?
  1. Bernard Preston
  2. Rainwater harvesting model
  3. Suburban rainwater tanks

Roof area

The factors to consider are the size of your roof from which you can harvest rainwater, and the length of your dry season.

It is relatively easy to collect rainwater from about half your roof area; it is certainly possible to harvest more, but it does get more difficult.

Let us say you have an average 200 m2 roof, and you are planning on harvesting from half of it; just for nice round figures, that makes 100 square metres.

That is about 1100 square feet.

If you have 100 mm of rain for say 10 months, then you can harvest about ten cubic metres of water every four weeks; 2649 gallons, depending on where you live naturally.

In the Sahara desert is would be rather less naturally

That is about enough for an average family, so assuming it rains at regular intervals, which it will not, of course, you could get away with a 2,500 litre tank for the wet season months.

One 5,000 litre suburban rainwater tank would provide enough storage for two weeks. If the weather is fickle for a month, and you can top up from the utility, then you would be fine.

If not, to be safe, you would need 10 kilolitres of storage, or 2649 gallons, to be more exact.

That is two large 5,000 litre tanks, each about five times the size of that shown above.

Dry season

But of course there is going to be a dry season, lasting say three months when you may not have a drop of rain; then you are going to need 30,000 litres of storage, if you are unable to access municipal water.

In our case, we almost always get some winter rain, so we planned for 27,000 litres of storage.

That means you would need six 5,000 litre suburban rainwater tanks.

Only once in nearly seven years have we run short, when the spring rains were later than expected; by one month. For this reason, we remain connected to the utility, though we use almost none.

Suburban rainwater tanks

Suburban rainwater tanks recommends you store your harvest from the skies underground because it is so much colder, and less unsightly.

Yes, the temperature of the water in above ground storage chambers, even if they are made of concrete, rises quite high, and unfriendly bacteria may flourish; it will certainly not be potable. 

You will have to rely on bottled water for drinking.

Underground reservoir

Our complete rainwater reservoir.

Whilst I am not a disbeliever in suburban rainwater tanks, we now have five at our home, for mass storage we think an underground reservoir is a cheaper and better solution.

One would need to get an engineer to draw up plans, or I might in the future provide ours as an eBook; dig a large hole and have a contractor lay a foundation with reinforcing.

Then build a double brick wall, with reinforcing, which would need to be plastered. It was surprisingly inexpensive.

Admittedly I did the plumbing and the electrics from our solar generator myself. But even so, it is not a lot of money to invest in an underground reservoir and to connect it into your home and garden.

It is a sublime supplement to your suburban rainwater tanks.

Underground the water is seriously cold, which means it is probably potable. We drink it without reservation, and have done so for more than six years.


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It is lovely and soft, and free of chlorine. One could put in an ozone or UV device to sterilize it.

It also tastes a lot better than chlorinated water from the utility.

There is a strong body of scientific thought that we have been amiss in trying to sterilise everything in our environment. There are a great many good bugs that help develop our immune systems.

It is astonishing that there are nearly five pounds of friendly bacteria, fungi and viruses in the normal alimentary canal; with twice as many cells as in a whole human body. Post chlorination can have a devastating affecting on this community.

You cannot grow vegetables and fruit trees without water. Harvesting and using suburban rainwater tanks for storage, or a reservoir, is absolutely essential for any form of backyard permaculture.

A strong base

Base for suburban water tanks.

First you must set a sturdy and strong base for your suburban water tanks, capable of supporting five tons. Strengthen it with a wire, using a puller to tighten it.

Fill the base with clay-type soil and compact it with a stamper. Then the tanks can be placed in position on the bases.

Simply making the reservoir one metre deeper, really at a small expense, would have saved us a lot of schlep.

Three suburban water tanks.

These extra water tanks were added after a particularly long winter drought lasting nearly six months. Now we should have enough no matter how arduous climate-change becomes.

Backyard permaculture

Working with nature, rather than against it, is the essence of backyard permaculture; it means having a reliable source of water in the dry season. If you are a serious gardener then harvesting and storing enough rain becomes a priority. 

Ours is in the winter, lasting about three months long, though the odd shower is not unusual; without some form of suburban rainwater tanks for storage it would be a hopeless pipe-dream.

There would be no lettuce, or cabbage, broccoli, kale, or broad beans. All demand a copious supply of water during the dry winter months.

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