A water-powered backup needs an uninterrupted supply with pressure and flow its manual requires. Liberty's SJ10 guidance explicitly says it will not operate during a power outage when supplied by a well pump. Do not count residual tank pressure as assured backup. Confirm the actual supply, backflow protection and discharge before choosing a water-powered system over an approved battery backup.
Check which supply survives the outage
Water-powered does not mean independent of the home's water source. This answer uses Liberty's SJ10 SumpJet and Zoeller's 540 FLEX instructions as documented examples. Identify the actual backup model and where its driving water comes from before purchasing.
The SJ10 product guidance says the pump needs an uninterrupted source and explicitly states that it will not operate during power outages if supplied by a well pump. Its installation manual describes a municipal-water emergency backup for clear sump water, not a replacement for the primary pump.
If your well pump depends on electricity, do not count remaining pressure in a tank as a verified outage supply for the backup. Ask the designer to assess the complete supported arrangement, or compare an approved battery-powered system instead. A plan must address the same loss of power that stops the main sump pump.
Check pressure while water is actually moving
Having water at a nearby faucet is not a performance check for a proposed backup. The manufacturer's required inlet flow, pressure, supply route and pumping height all matter.
The 540 FLEX manual specifies incoming pressures with its valve open as well as a separate maximum with it closed. Liberty also provides operating-pressure and performance guidance for its own pump. Do not substitute a static reading, a different manufacturer's figures or an advertised removal ratio for the applicable assessment.
Have the installer account for restrictions, backflow equipment and other water use under the actual installation conditions. Do not raise household pressure or connect a temporary garden hose to make a backup seem adequate.
Protect the drinking-water connection
The SJ10 manual says sump water is non-potable and requires the installer to provide the additional backflow protection required by local plumbing rules or the water authority. Its internal check valve is not a universal substitute for that approval.
Confirm the permitted assembly, accessibility and applicable maintenance requirements with the installer and authority. The backup also needs a documented, approved discharge route. Sump discharge planning addresses the destination; the manufacturer's connection directions still control the actual equipment layout.
Choose for the actual failure you need to cover
Municipal supply can also be interrupted. A water-powered unit cannot pump without its required driving supply, and prolonged use consumes supplied water. Do not treat the lack of a battery as a promise of unlimited protection.
Battery backup selection has different limitations. Regular maintenance still matters for either option. First confirm that the property genuinely needs a clearwater sump; a sewage ejector requires a different solution. Keep the selected manual and the supply, backflow and discharge assessment with the installation records.