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Rainwater tanks and pumps

A tank is sized by roof area and what you intend to use it for, not by the space in the yard — and the pump fails long before the tank does.

Roof area first, then use, then space

Tank sizing goes wrong when people start from the gap beside the house. The honest order is: how much water your roof actually collects (roof catchment area against local rainfall), what you are going to use it for (garden only, toilets and laundry, or whole-of-house), and only then what fits.

A tank plumbed to toilets and laundry needs to keep supplying through a dry spell, which usually means either a bigger tank or an automatic mains switch. A garden-only tank can run empty without anyone caring. Those are different tanks.

The first flush diverter is the cheapest water quality device you can fit. The first water off a roof carries the dust, leaf litter and bird droppings that accumulated since the last rain; a diverter dumps that volume before the rest enters the tank. Combined with gutter mesh and a screened inlet, it is most of what keeps a tank clean.

Pumps are the part that fails. A pump that starts and stops repeatedly while a tap runs steadily is short-cycling, usually a failed pressure vessel or a leak on the outlet side. A pump that runs but delivers nothing has usually lost prime or has a blocked foot valve or strainer.

If anyone in the house might drink it, read water quality first. We never call tank water potable on this site — that is a decision for a NATA-accredited laboratory test and your state health guidance, not for a web page.

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Sources

What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.