Fresh Water Pumps

By BoatUS Editorial Staff

The variations of fresh water pumps for use on a boat seem endless. How do you choose the right pump? Let's explore several factors that influence pump selection.

Open Flow

This can often be a misleading measurement, as most people assume that the larger the open flow capacity, the better the pump. But water-conserving faucets and fixtures allow only a measured amount of water to flow through. Water flowing through a fully opened faucet or shower generally causes about 30 PSI of back pressure, and can be as great as 55 PSI. An oversized pump in a system will result in erratic pump cycling, pulsating water flow, temperature fluctuations, and excessive power consumption as the pump starts and stops. Choose a pump that allows lower flows at higher pressures.

Power Consumption

Motor design, motor efficiency, and pump cycling are a few important factors to be considered with power consumption. The amp draw rating on the box is not always the best indicator of consumption, as it is usually given at open flow or at a low PSI rating. Amp draw charts provide more realistic information, showing power consumption at various pressures throughout the operating pressure range. Pump cycling can cause tremendous power consumption: starting and stopping of the pump creates "spikes" in the amp draw, with consumption highest at shut-off. Some cycling can be so severe that lights will flicker and some electronic devices will malfunction.

Safety and Reliability

Safety and reliability are related issues in that the marine environment is highly unforgiving. A Marine UL Listing assures you that the pump has undergone some of the most strenuous safety and reliability testing that exists.


Make sure that the pump you choose has a switch that's protected from the environment, as the switch is quite vulnerable to corrosion. Recently pumps have been marketed with switching that involves microprocessors which are supposed to keep the rate of flow constant. However many of these have been known to prematurely fail due to, in part, inadequate heat dissipation.

Installation and Serviceability

Installation, routine maintenance, and repair are often overlooked in selecting a pump. A pump that can be taken out of the box and installed or serviced without the need for a professional mechanic is most desirable. Most pumps today, such as, for example, the wobble plate 3 or more valve pumps by SurFLO are easily repaired with their repair kits and are essentially plug and play as to plumbing.


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