Water-Powered Backup Sump Pump: Pumping Without Power

What a water-powered backup sump pump is

Most basements with a sump rely on an electric pump. FEMA notes basements can flood when the primary pump stops working, when the power goes out, or when heavy rain overloads the pump ⁴. A water-powered backup pump covers the first two of those cases without a battery or generator.

Liberty Pumps describes its SumpJet as an emergency backup to an existing pump system that uses the municipal water supply to remove water from the sump, and says it is not meant to be the primary pump ¹.

It sits above or beside the main pump, with its own float and its own discharge pipe.

These pumps are a niche product. An ICC code proposal from 2014 names three makers of listed water-powered sump pumps at that time: Liberty Pumps, A.Y. McDonald and Zoeller ³.

How a water-powered pump moves water with water

These pumps have no motor. Pressurized supply water does the work, which is why makers list a minimum pressure and a rate of water use ¹².

1. Water rises in the pit: The main pump has failed or lost power, so the level climbs past its usual cut-in point.
2. The backup float lifts: A float set higher than the main pump’s opens a quick-acting valve on the city water line ¹.
3. Supply water rushes through: Pressurized water flows through a narrow passage in the pump body.
4. Sump water is pulled in: The fast stream creates suction that draws sump water up through a suction pipe and strainer ².
5. Both go out together: The mix of supply water and sump water leaves through a separate discharge line ².
6. The float drops: When the pit is drawn down, the valve closes and city water stops.

Which kinds of backup sump protection exist

Example: how much water one pump moves at your pressure

This example uses Liberty’s published SumpJet Table 1, measured with water flowing at the pump inlet ¹. Lift is the height from the pit to the highest point of the discharge pipe. The chart below shows the 8-foot column; the table shows how the same pump does at shorter and taller lifts.

Lift matters as much as pressure: at 30 psi the pump removes 12.8 gpm at 4 feet but only 5.5 gpm at 12 feet, and Liberty lists no rating at all at 20 psi above 8 feet ¹.

Worked case: a home with 40 psi flowing pressure and an 8-foot lift could expect about 12.5 gpm of sump water removed, by this table.

Using Liberty’s rule of about 1 gallon of city water per 2 gallons removed, that is very roughly 6 gallons a minute from the water supply while it runs ¹.

Liberty notes an RP/RPZ backflow device may lower operating pressure, so measure flowing pressure after the device, not just static pressure at a hose bibb ¹. Read our residential water pressure page for how to test.

Where it fits, and where it does not

It fits a basement with a working electric sump pump, a city water supply with good pressure, a cold water line nearby, and a place to run a separate discharge pipe outside. Liberty says the unit is designed for use with a municipal water supply ¹.

It does not fit a home on a private well. A well pump runs on electricity, so in a power outage the water pressure that drives the backup pump goes away too. Our page on the residential well pump explains that system.

It also does not fit a pit that collects sewage. Liberty says the pump is for clear water only, not waste water, sewage, effluent or water with debris ¹. Sewage pits use a sewage ejector pump instead.

Why people choose one, and what to weigh

Which limits to plan around: lift, efficiency and city pressure

Capacity falls as lift rises and pressure drops. In Liberty’s table, the same pump at 30 psi removes 9 gpm at 8 feet of lift but only 5.5 gpm at 12 feet ¹. If heavy rain sends water into your pit faster than that, the backup will fall behind.

Efficiency claims are not uniform.

A 2014 ICC proposal says the earlier green-code requirement of 2 gallons pumped per gallon used at 8 feet was "beyond the current state of the art" and proposed the IAPMO PS 119 figure of at least 1.4 gallons pumped per gallon used, at 10 feet and 60 psi ³.

Compare labeled ratios, not ad copy.

Pressure can sag during a regional outage if the water utility loses pumping. We found no data on how often that happens, so ask your utility how it keeps pressure during power failures.

What drives the cost of a water-powered backup

We do not list prices; fair numbers need dated local quotes.

The main drivers are the pump model, the backflow device your code requires (a reduced pressure zone assembly is larger and may need yearly testing), how far the nearest cold water line is, running a new discharge line through the wall, a separate shutoff valve and check valve, a high-water alarm, permit and inspection fees, and the city water the pump uses when it runs.

For the main pump and the rest of the pit, see our sump pump and basement water service page, and our plumbing cost guide for how quotes are built.

How a water-powered backup is installed

This connects drinking water to a pit of dirty water, so it is a job for a licensed plumber and often needs a permit. The manuals list these requirements:

1. Check the code: Ask which backflow device your plumbing code or water utility requires ¹².
2. Check pressure and pipe size: A.Y. McDonald calls for 29 psi running pressure and at least a 3/4 inch supply; Liberty recommends 3/4 inch pipe and 30 psi ²¹.
3. Add a shutoff: A dedicated shutoff valve on the supply within 6 feet of the pump, per A.Y. McDonald’s PS 119 notes ².
4. Install backflow protection: Such as an RP/RPZ device, as required locally ¹².
5. Use permanent piping: Liberty says never a garden hose; use copper, PEX or CPVC ¹.
6. Run a separate discharge: Not tied to the primary pump’s line or the sanitary drain ¹².
7. Set the float above the main pump’s cut-in point and add a water hammer arrestor if required; Liberty notes its quick-acting valve needs one under the UPC ¹.
8. Test: Fill the pit and watch it run, then shut it down.

The system view below gathers the parts the two manuals call for around the pump; an inspector will look for each one.

How to keep a water-powered backup ready

• Run it by hand once a month if it sits idle, as Liberty advises, and check that the float moves freely ¹.
• Clean debris from the float and suction screen ¹.
• Have the backflow device tested on the schedule your water utility sets.
• Keep the supply shutoff open; a closed valve means no backup.
• Test the primary pump too. North Dakota’s guide suggests slowly pouring about 5 gallons into the pit and watching the pump cycle at least twice ⁵.

Which signs mean the backup or main pump needs a plumber

• The backup runs often, which means the primary pump may be failing.
• Water keeps flowing from the supply after the pit is empty.
• The backflow device leaks or discharges water.
• Low flowing pressure in the home, below the pump’s stated minimum ¹².
• The high-water alarm sounds.

If water is rising in a basement, see our plumbing emergencies guide.

Which codes and standards apply: backflow, PS 119 and green codes

Backflow: Liberty’s 2018 manual says the Uniform Plumbing Code and the plumbing codes of some states, including Michigan, require an RP/RPZ backflow device for this product ¹.

A.Y. McDonald’s manual calls for a listed backflow device suitable for the installation, such as an RPZ, per local code ².

The IAPMO 2012 Green Plumbing and Mechanical Code Supplement, as quoted in an ICC proposal, requires a reduced pressure principle assembly on water-powered stormwater sump pumps ³.

Product standard: IAPMO PS 119, Water-Powered Sump Pumps. The 2012a(e1) revision sets a minimum efficiency ratio of 1.4 at 60 psi and 10 feet of head ³.

Green codes: The 2014 proposal (GEW161) to the International Green Construction Code would allow water-powered pumps only as emergency backups to an electric primary pump, with an 85 dB alarm, and would require the efficiency ratio to be marked on the pump ³. It is a proposal; check what your jurisdiction adopted.

Water hammer: Liberty notes its quick-acting valve requires an approved water hammer device under the UPC ¹.

How a water-powered backup compares with a battery backup

Which water-powered pump beliefs are wrong

Myth A water-powered pump can replace an electric sump pump.

Reality Makers and code proposals limit it to emergency backup ¹³.

Myth It uses no water worth noting.

Reality Liberty rates its pump at about 1 gallon used per 2 removed ¹.

Myth A garden hose is fine for the supply.

Reality Liberty says a hose can leak or burst; use permanent piping ¹.

Myth The built-in check valve is enough backflow protection.

Reality Liberty calls it nominal protection and says more may be required, such as an RP/RPZ ¹.

Myth It works anywhere with running water.

Reality It needs municipal pressure; it will not work on a private well when the power is out ¹.

Why your water source and code change the answer

Is a water-powered backup right for you?

It suits homes on city water with good pressure, frequent power outages, and a sump that runs often in storms. It is less suited to homes on a well, low-pressure areas, or places where the backflow device would be hard to fit or test.

If the pit floods even with the power on, the fix is more primary pump capacity, not a backup. Otherwise, start by measuring flowing water pressure and asking your water utility what backflow device it requires. Then compare it with a battery backup for your pit.

Related terms

Sump Pump

A sump pump is an electric pump that sits in a pit, called a sump, in the lowest part of a basement or crawlspace and pumps out groundwater that drains into the pit before it can rise onto the floor.

Backflow Prevention Device

A backflow prevention device is a fitting, valve assembly or air gap placed in a water line so that water can flow only one way, keeping used, chemical or dirty water from being pushed or siphoned back into the drinking water supply.

Cross-Connection in Plumbing

A cross-connection in plumbing is any actual or potential connection between a drinking water line and a source of pollution or contamination, such as a hose in a chemical bucket, a boiler fill line or a lawn sprinkler system.

Plumbing Check Valve

A plumbing check valve is a one-way valve that lets water or wastewater flow in only one direction and closes automatically, using a hinged flap, spring-loaded disc or ball, when flow stops or tries to reverse, so the pipe cannot drain backward.

Electronic Water Leak Detection

Electronic water leak detection is the use of battery or plug-in devices that sense water where it should not be, or track how much water flows through the pipes, and then sound an alarm, send a phone alert or close a valve when they spot a likely leak.

Main Water Shutoff Valve

A main water shutoff valve is the valve on the pipe that brings water into a house, placed near where that pipe enters, that stops the flow to every fixture at once so a leak or repair can be handled without calling the water utility.

Plumbing Flow Rate

Plumbing flow rate is the volume of water that moves through a pipe or out of a fixture in a set time, usually stated in gallons per minute (gpm), and it is what decides how fast a tub fills or how strong a shower feels.