Three pumps determine whether a household can stay in the house during an outage, and each of them is a modest electrical load.
The well pump
On a private well, no pump means no water at any tap and no flushing.
Submersible pumps are typically 1/2 to 1-1/2 hp, drawing perhaps 900 to 2,000 watts running with a starting surge of two to three times that.
The surge is what matters for generator sizing, and it is frequently the largest single surge in the house after air conditioning.
A pressure tank holds a small reserve — enough for a few minutes of use, not for a day — which is why the pump has to run.
Constant-pressure and variable-speed well pump controllers start gently and are much easier on a generator than a conventional pressure-switch pump.
The sewage ejector or septic pump
Where the drainage cannot flow by gravity — a basement bathroom, a septic system with the field above the tank, a low-lying house — a pump moves it.
If it stops, the household stops using water within hours, or discovers the problem the unpleasant way.
Loads are modest, typically comparable to a sump pump, and the consequence of omitting it is out of proportion to the watts.
Not every septic system has one. A conventional gravity system does not. Knowing which kind the house has is the first step, and it is not always obvious.
The sump pump
Where a basement relies on one, an outage during heavy rain is precisely the failure case.
The load is small — commonly 800 to 1,050 watts running, with a starting surge — and the consequence of losing it is a flooded basement.
A battery backup sump pump is a separate and worthwhile layer, because it covers the gap before a generator starts and the case where the generator itself fails.
Why these are non-negotiable on the essential list
They are the loads that determine habitability rather than comfort.
A household can cook on a camp stove, read by torchlight and wear a coat. It cannot function without water or drainage, and it cannot ignore a rising sump.
Sizing around them
All three are induction motors, so starting surge governs.
Since only one surge is counted in the sizing calculation, the question is whether two of them could plausibly start at the same moment — a well pump and a sump pump during a storm is a realistic coincidence.
Where the sizing is tight, staggering them electrically or accepting the risk is a design decision worth making explicitly.
The other water considerations
An electric water heater is a large load and hot water is a comfort rather than a necessity. It is the best shedding candidate in the house.
A whole-house water filter or softener with an electric control valve will not regenerate without power, which is a minor issue over a few days.
Frozen pipes are the real risk in a winter outage, and they are prevented by keeping the heating running — which is why the furnace or air handler sits alongside these three at the top of the list.
The check worth doing now
Find out whether the house has a sewage ejector or a septic pump, where the sump pump's circuit is, and what the well pump's nameplate says.
Those three facts are the beginning of the load list, and households frequently discover during the exercise that one of them is fed from a circuit nobody had identified.
Conserving during an outage
Every gallon pumped is energy, and on a generator running on stored propane that is fuel.
Households on a well during a long outage generally reduce use deliberately — shorter showers, full loads only, no watering — which extends both the fuel and, in a drought, the well itself.