ResilienceSeptember 27, 20266 min read

Water and power fail together

People buy a generator one year and think about water another year. Then the event arrives and it turns out they were always the same plan.

The short version

On a well, the pump stops and the water stops — immediately. Municipal at ground level usually keeps flowing.
A pressure tank holds far less usable water than its rating. The drawdown is a fraction of the volume.
The common design mistake: a tank bought for outages, pressurized by an electric pump. It fails in exactly the event it was for.
Make sure one path to water needs no power at all. That makes everything else optional rather than load-bearing.

People plan for these separately. They buy a generator one year and think about water another year, and the two plans never meet. Then the event arrives and it turns out they were always the same plan.

The reason is mechanical and not very interesting, which is probably why it gets missed: almost every way water moves in a modern house involves a motor.

Cutaway illustration of a home water storage system: a buried potable tank outside, a booster pump on a pad, treatment tanks and an ultraviolet chamber feeding the house. — Illustration — the booster pump between the tank and the house is exactly where the power dependency sits. Stored water still has to be pressurized to be any use. The fill arrangement varies by jurisdiction and is settled before anything is installed.

Where the dependency actually sits

It differs sharply depending on where your water comes from, and this is the distinction that matters most.

Your supply	When the power goes out	How long you have
Municipal, ground floor	Water usually keeps running on system pressure	Often through the whole outage
Municipal, upper floors of a tall building	Booster pumps stop; upper floors can lose pressure	Immediately, above the pressure line
Municipal, with a household booster pump	You lose the boost, not the supply	Reduced pressure, still flowing
Private well	The pump stops. The water stops.	Whatever is in the pressure tank. Minutes.
Stored water with an electric pressure pump	The tank is full and you cannot move it	Until you find buckets

Read the last two rows together, because that is the trap. A household that bought a water tank specifically for outages, and pressurizes it with an electric pump, has built a system that fails in exactly the event it was bought for.

On a well, this is the whole conversation

A submersible well pump is not a small load. It is a motor lifting water out of the ground, and it draws accordingly — which puts it in a different category from the lights and the refrigerator when you are sizing anything that has to run it.

What you actually have when the power fails is the pressure tank, and a pressure tank holds far less usable water than its label suggests. A tank is rated by total volume; the water you get out before pressure drops below useful is the drawdown, and it is a fraction of that. In practice, a few flushes.

Which means on a well property there is no meaningful difference between a power plan and a water plan. They are one plan, and it has to answer the pump question.

The honest menu

Stored water plus gravity

The only option on this list that needs no electricity at all. An elevated tank, or a tank with a gravity draw point, gives you water when everything else is off. It does not give you household pressure — you are filling containers, not taking showers. Unglamorous and completely reliable.

Stored water plus a small DC or battery-backed pump

Modest power, run from a battery, delivering real pressure for a limited draw. This is the proportionate answer for a lot of households and it is much smaller than people assume, because you are pressurizing from a tank at ground level rather than lifting from a well.

A generator sized to the well pump

The complete answer on a well property, and the most expensive one. It has to be specified against the pump's actual starting load, not its running load — motors draw substantially more at startup, and a generator sized to running load will not start it. PROFESSIONAL CONFIRMATION REQUIRED: this is an electrical sizing question for a licensed electrician, and any permanent installation involves a transfer switch and its own permitting.

Nothing, deliberately

A legitimate choice in town on municipal water at ground level, where the supply usually keeps flowing anyway. Know that you have made it.

The order to think about it in

Most people buy in the wrong order, which is generator first and water later. The sequence that produces a coherent system:

1. Establish whether you lose water at all. Municipal at ground level usually does not. Well does, immediately. Everything follows from this.
2. Decide what you need water for. Drinking and flushing is a container problem. Showers is a pressure problem. These have different answers and different costs.
3. Make sure at least one path needs no power. Whatever else you build, having one way to get water with everything off is the thing that makes the rest optional rather than load-bearing.
4. Then size the electrical. By this point you know what has to run, and the generator conversation is a specification rather than a guess.

Where we stop

We design and install water treatment and storage, and we will tell you plainly which parts of what we install need power and what happens to each when it is off. That is a question we think every vendor should answer unprompted and most do not.

We do not size generators, specify transfer switches or do electrical work. That is a licensed electrician's work, and on a well pump it is a real calculation rather than a rule of thumb. What we can do is tell you exactly what load our equipment presents, so whoever does that sizing is working from a number rather than an assumption.

We will tell you what needs power, unprompted

Every piece of equipment we install, what it draws, and what happens to it when the power is off. So whoever sizes your electrical works from a number.

Water resilience

Questions we get about this

Does my water stop when the power goes out?

It depends on your supply. On municipal water at ground level, water usually keeps running on system pressure through an outage. On a private well it stops immediately - the pump needs electricity and there is no municipal pressure to fall back on. Upper floors of taller buildings can lose pressure when booster pumps stop, and stored water with an electric pressure pump becomes unusable without power unless there is another way to draw it.

How much water is in my well pressure tank?

Less than the tank's rated volume. A pressure tank is rated by total volume, but the usable amount is the drawdown - the water you get out before pressure falls below useful - and that is a fraction of the rating. In practice it is a few flushes, which is why a well property's power plan and water plan are really one plan.

What size generator do I need for a well pump?

That is an electrical sizing question for a licensed electrician, and the key point is that it must be specified against the pump's starting load rather than its running load. Motors draw substantially more at startup, and a generator sized to running load will not start the pump. Any permanent installation also involves a transfer switch and its own permitting.

Can I use a water storage tank without electricity?

Only if it was designed that way. A tank pressurized by an electric pump gives you nothing during an outage unless there is a gravity draw point or another way to get water out. This is the most common design mistake in household water storage - a system bought specifically for outages that fails in exactly that event. Make sure at least one path to water needs no power at all.

Sources

Pressure tank drawdown versus rated volume is a standard characteristic of bladder and diaphragm pressure tanks; your tank manufacturer publishes its drawdown at given cut-in and cut-out pressures.
Generator sizing against motor starting load rather than running load is an electrical specification matter for a licensed electrician.