A delivery pump sits after the storage tank and pressurizes the water going out to the faucet or to an appliance. It is frequently confused with a feed booster pump, which sits before the membrane and does an entirely different job, and buying one when the other was needed leaves the original complaint exactly where it was.
What it fixes
Weak delivery. A reverse osmosis tank pushes water out using a cushion of compressed air behind a bladder, and that pressure is modest by design and falls as the tank empties. For a drinking faucet that is usually fine. It becomes a problem when the treated water has to travel any distance, feed a refrigerator ice maker that expects proper line pressure, serve a second outlet, or rise to a floor above. A delivery pump restores useful pressure at those points.
How it differs from a booster pump
A booster pump goes before the membrane and raises the feed pressure driving the reverse osmosis process itself, which improves production rate, rejection quality and the waste ratio on a low pressure supply. A delivery pump does nothing for any of that: the water it handles has already been made. If the complaint is that the system produces slowly, wastes a lot of water or has poor rejection, a delivery pump will not help and a booster pump is the correct purchase.
What comes with it
A power supply at the installation point, a pressure switch or flow switch so the pump runs only on demand, and often a small accumulator to stop it cycling rapidly. Pumps are audible, so siting matters in a quiet kitchen. Fit a check valve so pressurized water cannot push back into the tank. And confirm the wetted materials are suitable, since reverse osmosis water carries no minerals and is aggressive to some metals over time.
Check the cheap things first
Before buying any pump, empty the storage tank completely and check its air charge with a low pressure gauge, because a lost or wrong charge produces exactly the weak trickle a delivery pump is sold to fix and costs nothing to correct. Then check the tank isolation valve is fully open, the post filter is not choked and the tubing is not kinked behind the cabinet. Those four account for most weak faucets. Our reverse osmosis guide covers the full commissioning sequence.
Questions people ask about reverse osmosis delivery pump
What is the difference between a delivery pump and a booster pump?
A delivery pump pressurizes water leaving the tank. A booster pump raises feed pressure into the membrane and improves production.
When do I need one?
When treated water must travel a distance, feed a fridge ice maker expecting line pressure, serve a second outlet or rise a floor.
Will it improve water quality?
No. The water it moves has already been produced. Rejection quality is set by the membrane and the feed pressure ahead of it.
What should I check before buying one?
The tank air charge with the tank empty, the tank isolation valve, a choked post filter and kinked tubing. Those cause most weak faucets.