Your sump pump quits when the power does. Plan for that.

Quick answer: Your pump needs a second source of power and, ideally, a second pump with its own float and discharge line. A battery backup covers most outages. A generator covers long ones. A bucket and a wet-vac cover your nerves.

Heavy rain is the one job a sump pump has. Heavy rain is also the thing most likely to take down the line outside your house. The pump sits there, perfectly healthy, waiting for electricity that isn't coming, while the pit fills at the exact rate the storm dictates.

So don't ask whether your pump is good. Ask what it runs on when the lights are out.

Know what you've got

Go look at it. Take the lid off the pit with a flashlight and note four things.

• The pump itself. Find the label. You want the horsepower and the amperage, because you'll need both later.
• The float. It's the arm or the little ball that tells the pump when to start. Floats get snagged on the side of the pit more often than you'd think.
• The check valve. It's on the discharge pipe just above the pump. It keeps the water you've just pushed out from running back in.
• Where the water goes. Follow the discharge pipe outside. It should end well away from the foundation, and it shouldn't be buried under leaves, a snowbank or a flower bed somebody's wife planted over it.

Now test it. Pour a five-gallon bucket of water into the pit. The pump should kick on, empty it, and shut off cleanly. If it hesitates, chatters or runs without moving water, you've learned something for free on a dry afternoon.

An old pump is a gamble. If you don't know when it was installed, or the house came with it, treat it as a suspect.

Option one: a battery backup

This is the answer for most households. A battery backup system is a second pump, usually mounted a little higher in the pit, wired to a charger and a 12-volt deep-cycle battery. When the main pump loses power or can't keep up, the backup takes over.

The annoying part is run time. It depends on the pump, the battery, and how hard the water is coming in. A battery might run a pump for many hours if the pit fills slowly and the pump only cycles now and then. In a heavy surge, with the pump running constantly, it won't last nearly that long. Read the manufacturer's rated run time and plan for the shorter end.

Three habits keep it honest:

• Put the charger on a schedule you'll remember. Test the whole system a couple of times a year.
• Replace the battery on the manufacturer's timeline, not when it finally dies.
• Buy the high-water alarm. A battery-powered one that screams from the basement ceiling costs little and tells you the pit is rising before the carpet does.

A battery backup doesn't fix a clogged discharge line, and it doesn't help if the water table simply outruns your pump. It buys you hours. Use them.

Option two: a water-powered backup

This type runs on your home's water pressure instead of electricity. No battery, no charger, nothing to forget. It sounds like the perfect answer, and for some houses it is.

Know the catches first.

• It needs municipal water at decent pressure. If you're on a well, the well pump runs on electricity, so you've just moved the problem upstairs.
• It uses water to move water. Check the manufacturer's numbers for how much.
• Some towns restrict these or require a backflow preventer. Call your local building department before you buy one.

If you're on city water and your pit fills slowly, it's a solid second layer. If you're on a well, skip it.

Option three: a generator

A portable generator will run your main pump, your backup, a light and a fan. It's also what you want if the outage is going to last days, because batteries don't. The related piece on generator rules covers placement in detail. The short version is that a generator stays outdoors and well away from the house, always, because carbon monoxide doesn't care how hard the rain is falling.

Two practical points specific to sump pumps.

Motors draw more power to start than to run. The label on your pump gives you the running amps. Starting draw can be a good deal higher, so size the generator with room to spare. If you're not sure, ask the pump manufacturer or an electrician.

Don't backfeed the house. Never plug a generator into a wall outlet with a homemade double-ended cord. It can send power back out onto the line and seriously hurt a utility worker repairing it. If you want the generator to feed the house circuits, pay a licensed electrician to install a transfer switch or an interlock. For just the pump, a heavy-duty outdoor extension cord run to the pump's outlet is the simple route.

The catch with a generator is you have to be home, awake, and willing to go outside in the storm to start it. Keep fuel stored safely and fresh, and run it once in a while so you know it starts. A generator that's been in the shed since the last president's first term is a sculpture.

The manual layer

Something will go wrong with the plan. Have a floor under it.

• Keep a wet-vac, a five-gallon bucket and a length of hose where you can reach them without wading.
• Move anything you'd cry over off the basement floor. Plastic bins on shelves beat cardboard on concrete.
• Know where your main electrical panel is. If water is standing in the basement and you can't get to the panel without stepping into it, stay out. Call your utility or a licensed electrician. A flooded basement with live power is a different kind of emergency, and no box of photos is worth it.
• Keep a way to charge your phone and hear the forecast. The piece on radio when the internet goes down covers the second one.

Call your insurance agent before the rain

Most standard homeowners policies don't cover water that backs up through a sump or drain. That coverage is typically a separate add-on, and flood damage from rising water outside is a different policy again. Ready.gov and FEMA both point homeowners toward checking this ahead of time, since there's often a waiting period on flood policies.

Ask your agent plainly what's covered and what the deductible is. Then look at your emergency fund, because a deductible is a cash number and the bank may not be open when you need it.

Your Saturday

Pick one afternoon. Pull the lid, check the float, pour the bucket, trace the discharge pipe. Read the pump label and write the amperage on a piece of masking tape stuck to the lid. Then decide which of the three layers fits your house and your well-or-city situation, and put it on the calendar.

The pump has one job. Make sure it still has the power to do it when the rain's coming down and the street goes dark.