Connecting Multiple Water Tanks

Here are some helpful guidelines for when you are connecting multiple water storage tanks. Planning your rainwater harvesting system using this method maximises your available water without having to manually switch between tanks or install a transfer pump. You will end up with the simplest possible system, and best of all it automatically sorts itself out once you've set it up. Some very helpful pictures below show how the method works in practice.

Align tank overflows

First, align the heights of your tank overflows. Identically sized tanks are straightforward, but when connecting water tanks at different heights, smaller tanks need to be raised so that the bottom of their overflow is level with the bottom of the overflow of the largest tank in the chain.

Only one overflow in the chain is required provided it is at least as large as your downpipe. If you have multiple downpipes, you will need multiple overflows to match the incoming flows. Remember to match the heights of all overflows so that the bottom of each one is level. Overflows in excess of the incoming water can either be capped or simply connected to stormwater as well.

Link the lowest outlets

Link the lowest outlet of each tank with suitable flexible hose. Melro tanks are supplied with valves, and we recommend you use these to control the water from each tank. In a tank chain of three or more different sizes, start with the smallest (most elevated) tank and connect to the next largest tank in sequence.

Tap off the lowest tank

Water from all tanks will now drain into your largest tank during normal use. Simply connect your pump (or hose for gravity fed systems) to the bottom outlet of this tank.

Multiple Water Tank Connection Examples

Same sized tanks

The water tanks being connected in this image are the same height. Water flows into the first tank which has an overflow that at least matches the incoming water flow. You can choose to tap from either tank because the water level will automatically equalise between both tanks.

Connect same tanks

Differently sized tanks, different heights

Two tanks have been connected at different heights in this image. It does not matter which tank the incoming water flows into, it could also have been directed into the smaller tank.

Importantly, the smaller tank has been raised so that both overflows are at the same height. In this case the small tank's overflow has been capped because there is sufficient overflow on tank one, but it could also have been directed to stormwater too.

When the first tank fills above the base of tank two, the water level automatically equalises between both tanks. As water is used, water from the smaller tank's additional capacity automatically drains back into tank one. So, you only need to tap off the first (lowest) tank.

Connect different tanks