Choose a well pump by three things: how much water you need per minute, how deep the water sits, and the pressure you want at the taps. Water within 25 feet can use a shallow-well jet pump. Deeper wells usually use a submersible. Arizona wells need a licensed pump installer.
Is your well shallow or deep?
Pump type depends on how far down the water sits, and Goulds gives clear definitions. "A shallow well is one where the water is within 25 feet of the ground surface. A deep well is where the static water level is more than 25 feet down." The static level is the water level when the pump is off. When the pump runs, the level drops, which Goulds calls drawdown, and the level it settles at is the pumping level.
The 25-foot line comes from physics. A jet pump sits above ground and pulls water up by suction, and the manual gives this rule of thumb: "Practical suction lift at sea level is 25 ft. Deduct 1 ft. of suction lift for each 1000 ft. of elevation above sea level." Beyond that depth, an above-ground pump cannot lift the water by suction alone.
That leads to three common pump types.
Shallow-well jet pump. It sits above ground with one suction pipe running into the well, and it fits wells where the water is within suction range.
Deep-well jet pump. Goulds says the only basic difference from a shallow-well jet pump is where the jet assembly sits, which has to be placed so the suction lift from the pumping level stays within what atmospheric pressure can overcome.
Submersible pump. The whole pump and motor sit underwater in the well. Goulds says this means "the pump does not have to be primed," and water flows up the pipe once it is installed and turned on. It adds that submersible pumps are so much more efficient than jet pumps, and the installation so much simpler, that a submersible "should be considered first for all pump applications where the physical dimensions of the source of the water will accommodate the unit in a submerged position." Most submersibles, it says, are designed to fit four or six inch wells or larger.
For a deep Arizona well, that usually points to a submersible. Your well log will tell you the well's depth and casing, and your installer will check the pumping level before recommending anything.
How many gallons per minute do you need?
Start with the house. Goulds' manual gives a peak-demand table for private homes based on the bathrooms. The minimum pump size it lists to meet peak demand without a supplemental supply is 7 GPM for a home with one bathroom, 10 GPM for one and a half baths, 14 GPM for two to two and a half baths, and 17 GPM for three to four baths. Its notes say values are averages and that "peak demand can occur several times during morning and evening hours." Another note says to count the fixtures in the home, including outside hose bibs, and supply one gallon per minute for each.
Yard use adds to that. The manual lists a half-inch garden hose at 3 GPM, a three-quarter-inch hose at 6 GPM, and a lawn sprinkler at 3 to 7 GPM. A home with irrigation on the well needs a bigger pump than the bathroom count alone suggests.
Then check the well, because the well sets the ceiling. The University of Arizona guide says that for an exempt domestic well, "well pump capacity is restricted to 35 gallons per minute (gpm), but some aquifers are not able to yield water at that rate." It adds that "it is not uncommon for wells constructed in consolidated bedrock or finer-grained alluvium to yield 3 to 5 gpm." A pump that is bigger than the well can supply pulls the water level down and can start sucking air. The capacity measured when the well was built is in your well log, which the guide says every owner should keep.
A pressure tank helps with short bursts but not with sustained demand. The guide says the tank holds extra water so that small demands don't make the pump switch on, but "a tank cannot compensate for demand greater than your pump or well capacity." If your pump cycles on and off too often, see why a well pump short cycles.
What about pressure and horsepower?
Horsepower does not decide the choice by itself. Goulds explains that a submersible's capacity is largely set by the width of the impeller and diffuser, while pressure depends on the impeller diameter, the speed and the number of impellers. It gives an example: a half-horsepower pump with seven impellers, designed for capacity, delivers more water at 80 feet than a half-horsepower pump with 15 impellers, designed for pressure, but the second can raise water from a greater depth.
So two pumps with the same horsepower can behave very differently. The right one delivers your gallons per minute at your pumping level and at the pressure your pressure switch is set for. Installers read that from the pump's performance chart. Ask to see it. A pump that is big enough for your depth but rated for far more flow than the well can supply is the wrong pump.
Our guide on how a home well system works in Arizona explains how the pump, tank and pressure switch work together.
When should a well pump be replaced, and who does it?
Arizona's most common well failure is not a worn pump. The University of Arizona guide says: "The most common water supply well system failure in Arizona is due to dropping groundwater elevations." Its first warning sign is sediment building up in tanks, pipes and fixtures. Gritty sediment or sand in the toilet tank means you should contact a licensed well pump installer, and the guide says if the well keeps pumping gritty sand, the pump itself will grind to a stop and need replacing. If groundwater levels have dropped and air is entering the system, the guide says you may need the pump lowered or the well deepened.
That is why a new pump is not always the fix. A licensed driller can find out whether the pump is worn out or the water has dropped. The guide says a well's serviceable life is usually 20 to 30 years, and that "pump or plumbing failure should always be addressed by a licensed well professional."
After a flood, the EPA says to stay away from the well pump while it is flooded, to avoid electric shock, and to get help from a well or pump contractor to clean and disinfect the well before you turn the pump on.
Before you talk to an installer, gather your well log, the age of the pump, the pump's model number, what your water pressure and flow are like, and any changes you have seen, such as sand, cloudy water or air spitting from the taps. Those details let the installer choose the right pump the first time. Our page on common contaminants in Arizona well water covers what to test for while you are at it.