How to choose a self-priming pump for your garden
Suction lift has a physical limit, and pipe diameter matters just as much as pump power. Here's what to watch for with drilled wells and rainwater tanks.
A self-priming pump sits above ground and draws the water up. This makes for a convenient installation, but there's a physical limit: suction reliably works down to about 9 meters, and the deeper it draws from, the less usable head remains.
So the first question is never pump power, but the operating water level. If the water level sits deeper than 8 meters at rest, a self-priming pump is no longer the right direction — a borehole pump is the correct choice there.
Why suction drops off faster than you'd think
Suction doesn't load the pump 1:1. Every meter of depth eats into usable head, and on top of that comes friction in the suction pipe, which increases with the square of flow rate. At high flow rates the pump tolerates less suction, so even at shallow depths, a large draw-off can cause the water column to break.
In practice this means that above 7 meters you need to size carefully, and it's better to work with a wider suction pipe and a shorter suction run.
Pipe diameter matters as much as the motor
- Narrow suction pipe: high friction, reduced flow, cavitation. Go one size up in diameter instead.
- Long horizontal suction run: every meter and every elbow adds loss — keep it short and straight.
- Foot valve at the end of the suction pipe: keeps the water column in place, faster restart, less dry-running.
Drilled well or rainwater tank?
For a drilled well, both the static and dynamic water levels are decisive, because the level drops during irrigation. Factor in this drawdown, or a pump that looks adequate on paper may end up sucking air in practice.
For a rainwater tank, depth is usually small, so convenience features matter most: built-in pressure switch, dry-running protection, quiet operation. The JET PRO series, for example, comes with control electronics and protection built in from the factory, so you don't need to build automation around it separately.
Quick sizing checklist
- Depth of the operating water level (not the bottom of the well).
- Desired outlet pressure, in bar.
- Number of simultaneous consumers, which determines the required flow rate.
- Diameter and length of the suction pipe.
Once you have these, sizing takes only a few minutes. In the NERO Pumps pump selector you enter the parameters, and by interpolating on the performance curve you get a recommendation for a specific model, not just a general category.