Rain Tank Water

Lets look at some basic rainwater systems. Here is a picture of what a basic system looks like.

Simple it may look but there are some basic things we need to discuss here. One of the main things is what is the water going to be used for and water pressure.

I use my water for everything, drinking, washing, watering the garden etc. In the city you may not want to use it for drinking and it may be that the council will not allow you to. But, you can use it for everything else. This is where water pressure comes in.

I did a little experiment with one of my tanks which was full to the brim. (22,500 liters or, 5,000 gallons) It is a round tank 9ft (2750m) wide and 7 /1/2ft (2290mm) high.

I placed a 2 gallon (10 liter) bucket at the base of the tank and timed it filling up straight from the tank. It took 18 seconds. I did the same in the house sink where the water is delivered from the tank through a water pump. It took 23 seconds. All pipes were the same diameter with the exception of the pipe to the tap in the house which were half the diameter. Did this mean that the pressure straight from the tank was higher than that through the pump. No it didn’t as the house water was restricted by the diameter of the pipe and the tap outlet. Pressure is needed for a few things. One is so the valves in your toilets will deliver until they can fully close off the water when the cistern is full. The other is so that if more than one tap is turned on the pressure does not diminish from the taps.

Do you need a water pump to pump water to the house? Well this depends on how high above your taps the tank is. The higher the tank the greater the water pressure. This then poses the problem of getting the water into a tank that is raised off the ground. Later on this.

Also the lower the water level in the tank the lower the pressure.

As the inlet valve on a toilet is on the average about 700mm above the ground it is instantly obvious that if the water level in a tank sitting on the ground dropped below this then you would not get any water delivery if you did not have a water pump. The same with taps to basins which can be even higher. On top of this if you live in a double story house then the delivery problems are even worse.

By the way folks we are not talking about old fashioned toilets here. They are another problem.

So it looks as for any scenario you most probably will need a water pump in your rainwater systems.

It should also be mentioned that water delivery rate is also dependent upon the size and length of the pipe from the tank to the house. Water flow can also be affected by the number of bends in the pipe. Test this with a hose pipe. One that is still rolled up against one that is pulled right out. (dependant on what your water restrictions are of course on using a hose pipe)

Lets look at some more practical scenarios starting with a standard house on a standard flat block as applied to rainwater systems.

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