The spec that decides whether a battery or generator can start your pump is the one nobody puts on the front of the box.
Check the surge number →When a well loses power, the water does not stop instantly and that is the trap. The tap runs, weakens, and then quits, all inside a few minutes, and by the time most people understand what is happening they have already spent the only free water they were going to get. If you are reading this during an outage, go fill containers now and come back. The rest of this page explains how much you actually have, what to do with it, and what your options are for getting more.
Where the Remaining Water Comes From
Your submersible pump sits down in the borehole and stops the moment the grid does. It never pushed water straight to your taps, though. It filled a pressure tank, a steel vessel with a rubber bladder or diaphragm and a cushion of compressed air above it. That air is what pushes water into the house between pump cycles, and it is still doing it after the pump dies.
The catch is that the useful volume is a fraction of the tank’s rating. A captive-air tank delivers roughly 30 percent of its nominal capacity as drawdown between the cut-in and cut-out pressure settings. The rest is air. So:
| Tank size | Realistic drawdown | Roughly equals |
|---|---|---|
| 20 gallon | ~6 gallons | Four pour-flushes |
| 44 gallon | ~12-14 gallons | One short shower |
| 86 gallon | ~25 gallons | A day for two people |
Those are approximations and your pressure switch setting shifts them, but the order of magnitude is right and it is much smaller than people assume. If your tank has lost its air charge over the years, which is common and usually unnoticed, the real number is worse still.
The First Five Minutes
- Fill drinking containers first, at the kitchen tap, before anything else touches the plumbing.
- Then fill the bathtub and any large pots. That water is for flushing and washing, not drinking.
- Tell everyone in the house that the taps are closed until further notice. One long hand wash undoes all of it.
- Switch off the breaker for the well pump and the electric water heater.
- Do not run the dishwasher or washing machine, even if they seem to have started before the outage.
The breaker step matters more than it looks. When power returns, often at night and often with a voltage dip first, you do not want a pump motor and a 4,500-watt water heater element slamming on together while the utility is still stabilizing the line.
Do Not Drain the Water Heater Yet
There is a 40 to 50 gallon reserve sitting in your water heater and it is genuinely useful, but treat it as a second-day resource. Draw it from the drain valve at the bottom with the cold supply shut off, and only after the heater has cooled, because the first thing out of that valve on a hot tank will scald. The bottom of the tank also holds sediment, so the first gallon or two will look like weak tea. It is fine for flushing.
Flushing the Toilet Without a Pump
You do not need to refill the cistern. Pour roughly a gallon and a half of water straight into the bowl in one confident motion and the siphon does the rest. Bathtub water, rainwater, snowmelt, all fine. On a gravity septic system this works indefinitely. If your system has a pump chamber, effluent is accumulating with nowhere to go, so ration flushes hard and expect to keep rationing for a few days after power returns. That distinction is worked through in well and septic vs city water.
Getting the Pump Running Again
Three real options, in ascending order of cost.
A generator, sized for surge. A half-horsepower submersible runs at a few hundred watts but demands roughly 2,000 to 3,000 watts for the instant the motor starts. Three-quarter and one-horsepower units ask for more. Size on that surge figure or the generator will bog down and trip every time the pressure switch calls. Connect through a transfer switch, never by backfeeding a dryer outlet.
A large battery inverter. Increasingly viable, but only if the surge rating clears the pump. Plenty of mid-size power stations advertise 2,000 running watts and cannot start a 1/2 HP pump reliably. The efficient pattern is to run the pump for a few minutes to refill the tank, then shut it off, rather than leaving it energized.
A hand pump alongside the electric one. The only option that does not care how long the outage lasts. Deep well hand pumps from makers like Simple Pump and Bison Pumps install in the same casing as your submersible, typically needing 5 inches or more of casing to share, and reach static water levels around 250 to 325 feet depending on model. It is not cheap and it is not fast, but it is permanent. Match it to your well in hand pumps for wells.
Safety: Never run a generator in a garage, basement, crawlspace or breezeway, open door or not. CPSC attributes an average of close to 100 US deaths a year to carbon monoxide from portable generators. Outside only, at least 20 feet from the house, exhaust aimed away, and a working CO alarm on every level.
When Power Comes Back
Turn the well breaker on first, alone, and let the tank refill before you re-energize anything else. Run a tap until the water is clear and pressure is steady. If the water is cloudy, discolored or smells different than it did, stop using it for drinking until you have tested. And if the property flooded during the event, EPA’s position is unambiguous: do not use the well until a well or pump contractor has cleaned and disinfected it, then pump until clear.
The Honest Recommendation
If you take one thing from this page, it is that the cheap fix beats the clever one. Stored water costs almost nothing, needs no maintenance and covers the first two days completely, which is longer than most outages last. Buy the generator or the hand pump second, once you know your pump’s horsepower and your well’s static water level, because both of those purchases go wrong when they are made from a guess. Details on volumes and containers are in emergency water storage.
Frequently Asked Questions
How long does water last in a pressure tank after the power goes out?
Not in time, in gallons. Expect roughly 30 percent of the tank’s nominal size, so six gallons from a 20-gallon tank and around a dozen from a 44-gallon one.
Can I get water out of my well with a bucket and rope?
Almost never on a modern drilled well. The casing is typically four to six inches and already occupied by the pump, drop pipe and wiring. That trick belongs to old hand-dug wells.
Will a 2000-watt generator run a well pump?
Sometimes, for a small 1/2 HP pump, and only if its surge rating is meaningfully higher than 2,000 watts. Anything larger than 1/2 HP generally needs more headroom.
Is well water safe to drink after an outage?
Usually, if nothing flooded and the water looks and smells normal. Any flooding near the wellhead, or a change in appearance or odor, means disinfect and test before drinking.