# Measuring a Water Tank for a Replacement Liner A water tank liner is a great way to extend the life of a water tank that is still structurally sound but leaks water. Tank liners also have the added benefit in that further leaks are usually prevented as there is now a permanent membrane between the water any potential spot where a leak may form due to rust, cracking or ground movement.

Typical residential water tanks come in one of two shapes. Either they are circular or they are rectangular with rounded ends.

Making a tank liner for a round water tank is a fairly straightforward process. The only complication is if there are structural supports. These can be accommodated for, but the liner will have to be installed by a professional who can weld the liner around the struts.

With slimline and other similarly shaped water tanks, the process is only slightly more complicated in that the end shape has to be measured properly.

Other shaped water tanks are usually specialty water tanks and should be inspected by a qualified installer.

Measuring Any Round Water Tank

All that is needed to work out the size of the tank liner is the internal diameter (d) of the tank and the height (h) of the inside of the tank.

You can also use these measurements to calculate the volume of your water tank. This example assumes you are measuring in meters.

Calculating the volume of your water tank:

π x (d/2) x (d/2) x h   where π is pie = 3.14159

so for a 2 m high tank with a diameter of 5 m, the volume is them

= 3.14159 x (5 ÷ 2) x (5 ÷ 2) x 2 = 39.27 m3

The amount of water that can be held is then 39.27 x 1000 = 39,270 litres

Measuring a Rectangular Water Tank, eg a slim line Water Tank

Slim line Water Tanks are a little more difficult to measure, but not too much. To work out the size exactly, you just need to take into account the flat middle section and then both rounded ends. Each end of the water tank is like a semi-circle. I will assume each end is the same as this is usually the case. To measure you need:

h – height

d – width of flat middle section

a – width of water tank

b – distance from flat section to end of tank

volume is then:

2 x area of end pieces plus area of middle section

2 x π x (a/2) x (b) x h + a x d x h   where π is pie = 3.14159

so for a 1.8 m high tank, with a flat section that is 2 m long, is 800 mm wide and b is 500 mm.

2 x 3.14159 x (0.8 ÷ 2) x 0.5 x 1.8 + 1.8 x 2 x 0.8

2.26 m3 + 3.4 m3 = 5.66 m3

This means the volume of water that can be held is 5660 litres.