Pump priming is when water, or some other liquid, is used to draw up more liquid from a well that has already been tapped. While pump priming is not necessary with many modern pumps, there are times when it may be necessary, especially with older pumps. Therefore, knowing what to do and when to do it may be essential in some situations to ensure proper water supply.

Pump priming needs to occur when air has seeped down into the pump, replacing fluid and causing a loss of pressure. Most pumps use fluid, usually water, to create the pressure and suction needed to pull up more liquid from below ground. Therefore, when air seeps into the system, there is a loss of pressure.

In order to prime the pump, often all that is needed is another source of the liquid being sought. This is usually accomplished simply by pouring some of that liquid down the well. Once that is done, simply turning on the pump or using a hand crank, depending on the type of pump, is usually all that is required.

In most cases, once water starts to flow from a pump, more pump priming in the future should be unnecessary. However, in cases where use of the pump is suspended for a long period of time, more priming may be necessary. It is always best to try this method before assuming that the well has gone dry. This would be a very rare situation for a water pump.

If pump priming does not work the first time, it is advisable to do it again. It is possible that enough pressure was not created the first time the pump was primed. It may take several times before enough pressure is created to maintain a consistent water flow.

After a pump priming, it is recommended to allow the water to flow for a short period of time before collecting it for use, especially if the use is for human or animal consumption. This assures that stale, possibly contaminated, water that had been in the pump has been discharged. While the depth of the pump may make a difference, usually discharging no more than a gallon or two (3.78 liters to 7.5 liters) is all that is needed.

In addition to the technical usage, pump priming has become a metaphor for other things. When the government infuses money into the economic system, for example, it may be referred to as pump priming. The government hopes an influx of capital will help spur more capital movement. Thus, it is said the government is priming the economy.