Well pumps draw water from a well and send it into your house. These types of pumps are not the old-fashioned, long-handled pumps. They are electrically powered and don't require manual labor to operate. How much water those pumps draw is measured in gallons per minute, or GPM.
How many GPM your pump can draw depends on the pump that you own. Pumps use different size pipes and have different horsepower ratings. Generally, the larger the diameter of the pipe and greater the horsepower rating on the pump itself, the more water it will be able draw.
There are two types of well pumps: submersible and jet. A submersible pump is the most-common and works in deep wells. The pump is entirely submerged underwater in the well. The pump uses impellers that draw the water from the well and push it through the pipes to the house. Jet pumps have the pump motor and connections above ground and are good for wells that are no more than 100 feet deep, according to Lowe's. These pumps create a vacuum to draw the water from the well.
When a well is drilled, its capacity is determined. This is determined using the well driller’s log or a cleanout pump, according to Friesen Electric Company. The capacity is the rate at which water can be pumped from the well that allows the water level to recharge sufficiently.
According to Friesen Electric Company, the most-common types of pumps are: 5 GPM, 10 GPM, 20 to 27 GPM and 35 to 85 GPM. These are the gallons per minute that these pumps are rated to pump. In selecting a pump, don’t choose one that will draw more than your well can handle. If you overpump your well, you can ruin your pump if it is trying to draw water that isn’t there. Most homes will use the 10 GPM pump. Farms and ranches will need something larger, probably a 20 to 27 GPM pump.
To determine what pump capacity you need, simply allow 1 GPM for every fixture in the house, according to the Water Systems Council. Count the spigots in the kitchen, bathrooms, those used by appliances and those that are outside. Also count things with special fixtures like pools and hot tubs.