Choose a battery backup such as the Zoeller Aquanot Spin 508 if you want the most pumping power, have a well or low water pressure, or don’t want plumbing and code work. Choose a water-powered backup such as the Basepump HB1000-PRO if you are on city water with good pressure, lose power for days at a time, and your town allows it with the right backflow preventer.
Both kinds sit in the sump pit beside your main pump and start when the water rises past it. A battery backup runs a 12 V pump from a deep-cycle battery that a charger keeps topped up. A water-powered backup has no motor: city water pressure drives an ejector that draws sump water out with it. The one difference that usually decides it is what runs out first in your home: the battery, or the water supply and your town’s patience. We compare our top battery pick with our water-powered pick here; see every option in our backup sump pump comparison.
Run time in a long outage
About 5.5 h non-stop on one battery
As long as city water pressure holds
Pumping rate
1,800 gal/h at 10 ft on battery
About 1,000 gal/h at 10 ft, 60 psi
Where it works
Any home, on a well or city water
City water, 40 psi and a 3/4 in service
Water use
Uses no water
Uses city water each time it runs
Upkeep
Battery to check and replace; self-tests
No battery; test every 2 to 3 months
Code and install
Electrician advised for the wiring
Some cities ban them; backflow rules apply
Pit size
Pit at least 16 in by 22 in deep
Fits a 10 in sump
Choose the Zoeller Aquanot Spin 508 12 V Battery Backup Sump Pump System if you want the strongest backup flow, you're on a well or low pressure, or you'd rather avoid backflow rules.
Choose the Basepump HB1000-PRO Water-Powered Backup Sump Pump if you're on city water with 40 psi or more, outages last days, and your municipality allows it.
The flooding page puts backup pumps beside the other ways to keep a basement dry, and lists drainage pros in five cities.
Run time in a long outage
This is the water-powered unit’s whole case. A battery backup stops when the battery is flat: Zoeller rates the Aquanot Spin 508 at about 5.5 hours of continuous pumping on a 175-minute deep-cycle battery, and much longer when the pump only runs now and then. That covers most outages, but not a multi-day ice storm with a pit that fills every few minutes. The Basepump has no battery, so it keeps going for as long as city water reaches the house at enough pressure. The weak point is the same supply: if a storm takes out the water service, or pressure drops, the backup goes with it. Water-powered wins here.
Pumping rate
On flow, the battery pump is well ahead. Zoeller’s sheet gives 30 gallons a minute at 10 ft on a 12 V battery, about 1,800 gallons an hour, and 20 a minute at 15 ft. Basepump’s table gives the HB1000-PRO about 950 gallons an hour at 10 ft with 40 psi, 1,000 at 60 psi and 1,200 at 80 psi, so its output rises and falls with your water pressure. Neither is a substitute for a main pump; they are there to hold the line. If your pit fills fast in a spring melt, the battery pump buys more margin while it lasts. Battery wins.
Where it works
A battery backup works in any house with a sump pit and an outlet. A water-powered one needs municipal water: Basepump asks for at least 40 psi of static pressure and a 3/4 in water service and supply pipe, and suggests timing how fast an outside tap fills a 5-gallon bucket to check your flow. That rules out most homes on a private well, whose pump stops in an outage anyway, and many older homes with a 1/2 in service. Basepump’s smaller RB750-EZ may suit a 1/2 in service, but it is not the model we cover. Battery wins.
Water use
A water-powered pump spends clean water to move dirty water, and it only does so while it runs. Basepump puts it at about a gallon of city water for every 1.5 to 2 gallons removed, more at higher pressure. The City of Ann Arbor, which publishes a guide for owners of these systems, gives a less flattering figure of about 2 gallons of city water per gallon pumped, billed as ordinary use. The figures disagree, so take the maker’s as the best case. Either way it adds to the water bill in a long wet spell. The battery pump uses no water. Battery wins.
Upkeep
A flat or worn-out battery is a common complaint in owner threads about battery backups. The Aquanot makes that less likely than most: its controller charges in stages, tests the pump on a schedule and alarms on battery, charger, float and power faults. Even so, you will be buying a battery now and then; the Aquanot battery has its own three-year warranty. The Basepump has no battery, no charger and, Basepump says, no moving parts to service; it suggests a test every two to three months. If your town requires a testable backflow device, that testing is extra. Water-powered wins on day-to-day upkeep.
Code and install
Because a water-powered pump connects your drinking-water supply to the sump, plumbing rules apply. Basepump says most plumbing authorities require an approved backflow preventer; its PRO kit includes a brass dual check valve (ASSE 1024, CSA B64.6), and a vented version is sold for places that want one. Some cities ask for more, such as a reduced pressure zone (RPZ) device tested regularly by a licensed plumber, and a few don’t allow these pumps at all, so check with your municipality and a licensed plumber before you buy. The Aquanot needs no plumbing permit of that kind, though Zoeller advises a licensed electrician for the wiring. Battery wins.
Pit size
Space in the pit matters more than people expect. Zoeller asks for a pit at least 16 in across and 22 in deep for the Aquanot Spin 508, with the backup’s float set to switch off above the DC pump. The Basepump’s intake works in a sump as narrow as 10 in, and the ejector itself mounts on a joist or wall above the pit. If your pit is small and you want a battery system, look at the Basement Watchdog CITE-33 combo in our best battery backup sump pumps, which fits a 10 in pit. Water-powered wins here.
Which should you choose?
For most homes a battery backup is the simpler, stronger choice. A water-powered backup makes sense in a narrower case: good city pressure, long outages, and a municipality that allows it and is happy with the backflow device.
Choose the Zoeller Aquanot Spin 508 if…
- You want the most water moved per hour when the power is out
- You’re on a well, have low pressure or a 1/2 in service
- You’d rather not deal with backflow devices and their testing
Choose the Basepump HB1000-PRO if…
- You’re on city water with at least 40 psi and a 3/4 in service
- Outages in your area last days, not hours
- Your municipality allows it and has confirmed the backflow device it wants
Neither quite right? Compare every backup sump pump we cover, including the Liberty 442-10A and the Basement Watchdog CITE-33 combo. A backup pump won’t stop sewage coming up through a floor drain; that takes a backwater valve (our backwater valve guide shows how one region’s rules and grants work).
Water-powered backup questions
Does a water-powered sump pump work without electricity?
Yes. It runs on city water pressure alone, so it keeps working through a power cut of any length. It stops if the water supply fails or pressure falls below about 40 psi, and it is no help on a private well, whose pump stops in the same outage. Its water alarm runs on a 9 V battery.
Does a water-powered sump pump need a backflow preventer?
Almost always. Basepump says most plumbing authorities require an approved device where city water meets sump water, and its PRO kit includes a dual check valve. Some cities want a stricter device, such as a reduced pressure zone (RPZ) valve that a licensed plumber tests. Ask your municipality which one before you buy.
Are water-powered sump pumps allowed everywhere?
No. Plumbing rules are set locally, and some cities ban water-powered backup pumps outright, so ask your municipality first.
How much water does a water-powered backup use?
Basepump puts it at about a gallon of city water for every 1.5 to 2 gallons of sump water removed; one city guide for owners gives about 2 gallons per gallon pumped. It only uses water while it runs, but a long wet spell shows up on the water bill.
