The Rain Tank!


5m (16feet 3inches) long
3m (9feet 9inches) wide
1.2m (4feet) deep


Hole dug out = 18 cubic metres (635 cubic feet) about 38tons of sand and soil
Water inside is 95% of hole size = 17.1 cubic metres – due to the plastic construction of the crates
Overflow starts 50mm below top surface of tank so will never fill to maximum therefore subtract 0.72 cubic metres.
Plus the pump cannot reach right to the very bottom of the tank as the plastic crates has structural flanges which will contains a certain amount of water. The highest flanges are 50mm high so therefore that is another 0.72 cubic metres of unuseable water!
Total Storage for rain water is 15.66 cubic metres
That is 15,660 litres
3,445 gallons (UK measurements – its 4,137 US Gallons)
27,558 pints !

Now that is a big water butt!


There are 90 crates each measuring 1000mm by 500mm by 400mm (well actually it is 390mm high – the manufacturer states that each crate is 200litres capacity but in reality it is only 195litres!) made of a polyproperlene materials. We layered 15 crates on each layer and rotated them around to provide maximum loading spreading. There are 4 layers altogether. Then a thick geotextile (measured as 250gsm) is put on first to soften the edges of the crates (we also sanded the edges and especially the corners). The rubber membrane is the next layer (the rubber is a man-made material with long life stability, we decided to buy the 0.75mm thick grade. You could have 0.5 or 1mm thicknesses) and finally on the outer most an another layer of thinner but tougher geotextile (about 150gsm) to keep the sand and soil from wearing or puncturing the rubber!

So far we have 200mm of water in the tank and it is still there after a week! phew!


We can use it to flush our toilets, wash the car, have showers, provide automatic watering for the garden and even use it for the washing! We of course will have the normal Mains Water taps in the kitchen etc. for drinking.

By Shaun

Leave a Reply