Most Arizona homes do not need a sump pump. A sump pump removes groundwater from a basement or crawl space, and Valley homes rarely have a groundwater problem. You may need one if you have a below-grade room, or a lot near a wash or canal. A bathroom below the sewer line needs a sewage pump.
What does a sump pump actually do?
Zoeller, a pump maker, describes a sump pump as "a device that helps keep your basement or crawl space dry by automatically pumping out accumulated water due to rain or natural groundwater." Wayne, another maker, says sump pumps "are automatic pumps used to remove ground water from sump pits" and that "the most common application is for basement drainage to prevent flooding in residential buildings."
Notice what both descriptions have in common. They start with a basement or a crawl space and with groundwater. A sump pump is a fix for one problem: water that seeps in from the soil around a low structure and has nowhere to drain by gravity.
The pump sits in a sump pit, a basin set below the floor. A float switch rises as the pit fills and turns the pump on. The pump then pushes the water out through a discharge pipe. Our guide on where a sump pump can legally discharge covers where that pipe is allowed to end.
Why most Valley homes don't need one
Groundwater is the trigger for a sump pump, so the depth of the water table matters. The University of Arizona's well owner's guide says Phoenix and Tucson sit in the Basin and Range province, and that "increasing groundwater pumping continues to lower water table elevations" there. It also says that because of Arizona's arid and semi-arid climate, recharge to groundwater is estimated at 2% to 3% of the average annual rainfall.
Put those two facts together. Groundwater in the metro area is being drawn down, not pushed up toward foundations, and only a small share of the rain that falls ever reaches it. That is the opposite of the wet-soil conditions that make basement sump pumps common in other parts of the country.
Add the way a slab home is built. A house on a slab has no basement floor for groundwater to seep through and no low pit where it collects. Without those, a sump pump would sit in a dry hole.
Monsoon storms are a different problem. Heavy rain can flood a yard, a garage or a street within minutes, but that is surface runoff, and grading, drainage channels and retention basins deal with it. A sump pit under the house does not help. If your worry is water in a low garage or a yard that ponds, see how monsoon season affects plumbing and how to prevent a sewer backup before monsoon. Those are separate fixes.
When might an Arizona home need a sump pump?
Three situations can change the answer.
You have a basement or a below-grade room. Some Arizona homes have a basement, a sunken lower level or a below-grade room with a floor lower than the surrounding ground. If water shows up on that floor, or the soil outside stays wet, a sump pit and pump can be part of the fix. Wayne's manual names the standard case: basement drainage to prevent flooding.
Your lot sits near a wash, canal or other surface water. The University of Arizona guide says shallow wells near surface water or washes, "with a water-table within a few feet of land surface, may exhibit dramatic seasonal variation in water table depth due to rapid infiltration of recharge following precipitation or stream flow." Most Arizona wells, it adds, sit far from their recharge source and are less likely to show seasonal changes. The lesson for a homeowner is that a property right beside a wash can behave differently from one in the middle of a subdivision. If you have a low floor and live in that kind of spot, groundwater rising with a storm is a real possibility.
You need to move water out of a pit for another reason. Some properties collect water in a stairwell, window well or below-grade entry. These are small versions of the same job, and a sump pump can handle them if the water is clear and has somewhere legal to go.
If none of these describes your home, a sump pump is unlikely to solve anything. Grading and drainage around the house are the better places to look.
Is a sump pump the same as a sewage pump?
No, and this is the mix-up that matters. A sump pump handles clear water. It is not built for waste.
Wayne's manual says it flatly: "DO NOT USE SUMP PUMPS TO HANDLE RAW SEWAGE." It also says these pumps "are designed to pump clear water only."
Zoeller, a pump maker, draws the same line in its FAQ: if your home has bathroom facilities below the main sewer line or septic line level, "you will need a sewage pump to move waste to the higher elevation," and sump pumps "are only for removing groundwater and are not suitable for transporting solid waste."
That matters here because a pump in an Arizona home may well be handling waste, not groundwater. A finished lower level, a converted space or a low addition can put a toilet, shower or washer below the height of the sewer line. Waste from those fixtures cannot drain downhill, so a sewage ejector pump lifts it to the building drain. It is a different machine with a sealed basin, and it discharges to the sanitary side, not to the yard. Our guide on the difference between a sump pump, an ejector pump and a lift station sorts out the three, and what a sewage lift station is shows the same idea at a larger scale.
If you are unsure which one you have or need, ask before you buy anything. A plumber can tell in one visit whether the water is groundwater, waste, or something else, such as a leak. And if water is showing up on a floor with no obvious source, how plumbers find hidden leaks explains what to rule out first.
What should you do if you already have a sump pump?
Some Arizona homes do have one, and it needs to work when a storm arrives. Test it by pouring a bucket of water into the pit, as the manufacturers advise, and keep the pit cover on. Our guide on how to maintain and test a sump pump walks through the checks.
Two more points from the pump makers apply to any home with a below-grade floor. Wayne says "an independent highwater alarm or back up pump should be used when risk of property damage from high water levels exists." And the CDC's flood-preparation advice for homeowners includes "buy and install sump pumps with back-up power." If a lower level in your home is finished, that advice is worth taking seriously. Our page on whether you need a battery backup for your sump pump explains how a backup works and what it can and cannot do.
If you are still not sure whether your home needs a pump, or water keeps showing up on a low floor, HQ Plumbing and Air can trace it for you. Call any time, day or night. We are licensed and insured, and you get a free estimate and the price up front.