Startup surge on a submersible pump is the number that sets the whole backup budget, and most people guess it.
Size it properly →Well and septic vs city water is not a small detail of your house, it is the fork that decides half your outage plan. Two houses on the same road, same square footage, same furnace, will need different equipment, different stored volumes and a different first hour, purely because one is connected to a municipal main and the other owns its water from the aquifer up. Most preparedness advice online is written for the city house and then handed to the country one, which is how people end up with a generator that cannot start their own pump.
The Difference in One Table
| Issue | City water and sewer | Well and septic |
|---|---|---|
| Outage water | Hours to days of pressure | Tank drawdown only |
| Flushing | Usually works | Pour-flush by hand |
| Generator need | Optional comfort | Often the deciding load |
| Water quality | Utility tests it | You test it |
| Contamination | Boil notice issued | Nobody tells you |
| Repair cost | Utility’s side of meter | All yours |
Why City Water Survives an Outage and a Well Does Not
A municipal system stores pressure as height. Water sits in an elevated tank, gravity does the rest, and the utility’s own pumps run on backup power at the plant. Your tap keeps flowing through a neighborhood blackout because the pressure was created hours ago and is still sitting up in the air.
A private well has no such reservoir. The submersible pump sits in the borehole and pushes water into a pressure tank in your basement or well house. When the power stops, the pump stops, and what you have left is the tank’s drawdown. Not its nominal size: a captive-air tank gives up roughly 30 percent of its stated volume between the cut-in and cut-out pressures, so a 44-gallon tank is about 12 to 14 usable gallons and a 20-gallon tank is nearer six. That is the entire buffer. The full sequence of what to do with it is in when your well loses power.
Sewer vs Septic: The Quieter Half of the Fork
On city sewer, gravity or a municipal lift station moves your waste and neither is your problem. A conventional gravity septic system is arguably even better in an outage, because it needs no electricity at all: the tank settles solids, effluent leaves by gravity, the drain field does the rest. As long as you can get water into the bowl, it works.
The exception matters. If your drain field sits uphill from the tank, or you have a pressure distribution system or an aerobic treatment unit, there is a pump in the chain and it stops with the grid. Effluent accumulates in the chamber for the duration. State health department guidance is consistent: reduce water use sharply during the outage and for several days after, because when power returns an over-full chamber can dump a large slug onto the drain field at once. Also worth knowing before the storm arrives, not during it: find out which type you have.
The Generator Consequence
For a city house, a generator is largely about the refrigerator, the furnace fan and some lights. Those are gentle loads and a small inverter unit or a decent battery covers them.
For a well house, the pump changes the arithmetic. A half-horsepower submersible typically runs at several hundred watts but demands roughly 2,000 to 3,000 watts for the fraction of a second it takes the motor to start, and a three-quarter or one-horsepower unit asks for more. A generator sized on running watts alone will stall or trip when the pressure switch calls. This is also why many well owners run the pump deliberately, on a schedule, to refill the tank and then switch the breaker off again rather than leaving it live. Work through your own numbers in what size generator does your house need.
Water Quality Is Also Your Job
A utility tests continuously and has to tell you when something is wrong. Nobody does that for a private well. EPA’s guidance for well owners is to test annually for total coliform bacteria, nitrates, total dissolved solids and pH, and to test immediately after any of these:
- Flooding on or near the property, or nearby construction and industrial activity.
- Any repair or replacement of well components, including a new pump.
- A change in taste, smell or color, even if the water still looks fine in a glass.
- A new pregnancy, infant or immunocompromised person in the household.
Safety: After flooding, EPA’s advice is not to use the well at all until a well or pump contractor has cleaned and disinfected it and you have pumped until the water runs clear. Floodwater carrying septic or agricultural runoff into a wellhead is the classic way a rural family gets sick a week after the storm ends.
The Two Prep Lists, Honestly
City house: stored water for a boil-notice week, a way to keep the fridge and furnace alive, and a plan for the fact that a wide-area event can still take the treatment plant offline. That is a real scenario and worth respecting, but it is a rarer one.
Well and septic house: stored water as the non-negotiable first purchase, a generator or battery sized around the pump’s surge, water treatment you can run without power, and eventually a manual way to reach the water column. That last one is where a hand pump matched to your well depth earns its cost, because it is the only item on the list that does not care how long the outage runs.
Which One Is Actually Better
Neither, and anyone selling you one over the other is selling something. City water buys you convenience and outsourced testing, and costs you the ability to do anything about it when the utility has a bad week. A well makes you the utility: worse day-one resilience, far better week-two resilience, provided you have spent a few hundred dollars on the boring things. The mistake is owning a well and preparing like a city house, which is the default because that is what most of the internet is written for.
Frequently Asked Questions
Can I flush the toilet during a power outage with a septic system?
With a gravity system, yes, by pouring about a gallon and a half of any water directly into the bowl. With a pump chamber, keep flushes to a minimum until power returns.
How do I know if my septic system has a pump?
Look for a control panel or alarm box on an exterior wall near the tank, and a dedicated breaker labeled for the septic. Your county health department usually holds the permit drawing for the property.
Does a well pump need a generator or will a battery do?
A large inverter battery can do it if its surge rating clears the pump’s starting draw. Many mid-size portable power stations cannot, so check surge watts rather than continuous watts.
Is well water safe to drink without treatment?
Often yes, but only your own test results tell you, and only for the day the sample was taken. Annual testing is the minimum standard, and any flooding resets that answer to unknown.