Basement water questions arrive in two tenses: before the storm (how long will the backup run) and during it (the pump is silent and the floor is wet). These are the ones homeowners actually ask — sump batteries, stations versus pumps, well pressure, and the septic question nobody thinks of until the first flush. Short answers here, full math on each question’s own page where one exists. This shelf hangs off our Water hub.
The sump questions
How long will a sump pump battery backup run — and do you need one with a generator?
A typical battery backup system pumps for days of ordinary rain because the pump only runs minutes per hour — what drains it is a storm that keeps it cycling. And yes, it still earns its place next to a generator: it covers the hours the generator is off, out of fuel, or not yet started, and it starts itself at 3 a.m. without you.
Battery backup: Starts itself at 3 a.m. — days of ordinary rain.
A power station: Must clear the starting surge — 800–1,050 W running · 2,000 W+ to start.
The generator: Covers the long storm — the backup covers the hours the generator is off, out of fuel, or not yet started. The pump runs minutes an hour; a storm that keeps it cycling is what drains a battery. The backup earns its place next to a generator — not instead of one.
Can a power station run a sump pump?
Yes, if the station’s inverter clears the pump’s starting surge: a half-horsepower pump runs around 800–1,050 watts but can pull 2,000 watts or more for the second it starts, which rules out small stations even when their running watts look close. Runtime is a duty-cycle question — at a few minutes per hour, a 2 kilowatt-hour station stands guard for a day or more of ordinary rain.
The well and septic questions
Will I have any water in an outage on a well? What’s left in the pressure tank?
Only what’s stored in the tank under pressure — and it’s less than the tank’s size suggests. A 20-gallon pressure tank typically delivers about 5–7 gallons before the pressure is gone; after that, the well is silent until power returns. Knowing your tank’s real drawdown is the difference between rationing calmly and finding out at the tap.
The pressure tank: A 20-gallon tank delivers about 5–7 gallons — then the well is silent.
The ejector basin: The septic toilet’s reserve — a few flushes, not a day of normal use.
Past the reserve, flushing risks exactly the backup you are picturing. The ejector pump draws about what a sump pump draws — one sizing usually covers both.
Covered in: When the power goes out: the six problems every house has to solve
My toilet is on a septic ejector pump — can I flush in an outage? Will sewage back up?
The basin gives you a small reserve — a few flushes, not a day of normal use — because each flush needs the pump to empty what gravity can’t. Past the reserve, flushing risks exactly the backup you’re picturing. The fixes are the same as the sump’s: the ejector pump draws about what a sump pump draws, so the battery or station sized for one usually covers the other.
How we answer
Ordinary Prepper is a research desk, not a test lab: we do not claim hands-on testing. Pump draws come from manufacturer specs for typical residential sizes, battery runtimes from the duty-cycle math shown on the page, and tank drawdown from standard pressure-tank sizing — ranges are stated as ranges.