The thunderstorms, flash floods, tornado warnings and odd hurricane of the past few years have taught Tom Grein a hard-learned lesson: Expect the unexpected. Don't automatically assume your basement sump pump will keep you dry when the water starts rising.

Grein's initiation came by way of a downpour in 2002. "We woke up to find four to five inches of water in our basement," said the former Herndon resident. "Our kids bailed and bailed and bailed water for an entire Saturday. Then we had to put fans [in the basement] and take our ruined possessions out to the curb. It was devastating."

A plumber's post-mortem confirmed Grein's suspicions: dead sump pump, four years old. Replacement cost: $340.

The new unit worked like a champ -- until last September, when Hurricane Isabel knocked Herndon's power grid offline. No electricity, no sump pump.

"My wife was in the basement with a pail, literally bailing the water out of the sump pump [pit] as fast as she could," he said. "Because I use a wheelchair, I acted like a cheerleader at the top of the stairs. She would run up the stairs, hand me the pail and I would dump the water into the bathtub."

Been there, done that, Fairfax resident Ricardo Urdaneta said. In 2000, his sump pump conked out for a second time. A plumber's $90 fix coaxed two more years of life, until a thunderstorm overwhelmed it. Thrice stung, he began researching his options.

Today, the chastened man willingly shares his watery wisdom. "First," he said, "make sure your sump pump and rain gutters are discharging the water away from your house. Second, realize your sump pump has an electric motor that will eventually fail. Third, it's very possible that when you need the sump pump the most, you're at the highest risk of losing your power."

So, what backup system is best for keeping an at-risk basement dry? And what's the buzz on the latest technology -- an install-and-forget sump pump that actually fights water with water? Here's a look at the options.

Emergency Generators

As Grein and Urdaneta found, a sump pump stops working for two reasons. "Power failures are only 50 percent of the reasons basements flood," said Bill Bonifacio, president of Base Products Corp., a sump pump maker in Buffalo. "Your primary pump can also [mechanically] fail." If you only back up the power system, not the pump, you protect yourself only from power failures, he said. A generator alone won't back up the pump.

The gold standard, he said, is an independent system that provides backup power and pump capacity. Homeowners should decide how much redundancy they need.

According to Dominion Virginia Power, consumers snapped up an estimated 50,000 portable generators as Hurricane Isabel bore down on the region last year. Many cited sump pump worries as their motivation. Retailing at $450 or more, most portable power supplies can crank out enough amps to keep sump pumps cycling on and off until a storm passes. These units are easy to start, offer plenty of electrical outlets for extension cords, and do not require a plumber or electrician.

But Dominion spokesman Mark Fink offered a few caveats. "A portable generator," he said, "is not designed to operate outside during a driving rainstorm."

Without adequate shelter, the units are susceptible to engine damage, flooding out, and possible voiding of warranty. "Many consumers also don't know how to hook them up safely. We're also afraid someone will open their garage door, start [a generator] in the garage, and then go to bed." That can cause asphyxiation by carbon monoxide.

Another limitation: Unless a generator is hard-wired into a home's main electrical system, it must be manually activated when the primary power supply fails -- unlikely if you're asleep or at work. And even the most sophisticated systems are useless if the sump pump fails, as Grein's family learned. And while experts estimate a sump pump's lifespan at five to seven years, the Urdanetas discovered that the first warning sign is often a basement floor that goes splash.

Battery-Powered Backup

Despite spending their lives in dark, dirty holes, sump pumps are the unsung heroes of modern America, allowing homeowners to finish basements in ways once impossible. But even superheroes age and the time-honored precaution against unannounced retirement has been the battery-powered backup.

These systems come in two types: power inverters and complete battery-powered systems.

The power-inverter method so impresses Dominion that it features the $1,240 Sumpro on its Web site. By way of a large inverter, this feature-heavy unit converts its internal 12-volt DC battery power into conventional AC current -- the lifeblood of primary sump pumps. "It typically gets you 18 to 30 hours of use and is extremely popular in Northern Virginia," Fink said. Notably, the unit does not include a backup pump. (Until the manufacturer discontinued the product, Dominion featured the $1,295 SumpGenius, outfitted with both power and pump redundancy.)

As a caution to the desperate, Rick Rubeck, manager of Battery One in Frederick, Md., said power inverters found in late-model cars or trucks cannot satisfy a sump pump's hunger for amperage. "If it ran at all," he said, "it would only run for a short time."

Homeowners looking for total power-and-pump redundancy may consider a complete battery backup system ($140 to $800, retail). Available at home-improvement centers and through Internet dealers, these fully automatic units come equipped with a backup pump and hardware to connect them to a separately purchased marine battery. The marine aspect is critical, as these deep-cell batteries ($60 plus, retail) have the stamina to survive repeated drainings, unlike their automotive counterparts. An attached power supply, plugged into a standard wall outlet, keeps the batteries charged.

At the $300 level, two-battery systems offer audible and visible alarms, as well as heavy pumping capacity. Premium units nearing $900 boast remote alarms, self-cleaning features and daily diagnostics. Manufacturers advise professional installation.

Gary Eldridge, owner of Fairfax-based Homeowners Plumbing, cautions that these systems require periodic maintenance and the replacement of batteries every three years, used or not. "People just don't maintain their batteries," he said. "Many times, they discover during a rainstorm that it's dead." Dead battery, dead pump.

Water-Powered Sump Pump

If any system merits the title "latest and greatest," it's the water-powered sump pump, which is connected to the municipal water supply. A hot seller in the Midwest, the technology is only now making inroads into the mid-Atlantic region.

"It's a fantastic system," said Eldridge. "We've installed quite a few."

Base Product's Bonifacio said his company sells 30 water-powered systems for every battery system. "You install it and literally forget about it," he said.

Commenting on a backup technology that needs no electricity or battery, Robert Finegan, president of Tane Corp., said, "Many of our customers are former battery-powered owners."

Bonifacio said the technology uses the same vacuum principle that dispenses liquid fertilizer from a hose-end sprayer. By directing pressurized drinking water into the sump pit through a standard plumbing pipe, clean water essentially pulls the sump water out with it, as it is ejected from the house through a discharge pipe. Manufacturers claim that 60 pounds per square inch (psi) of water pressure -- typical of many residences -- translates into one gallon of fresh water per gallon of expelled sump water. (Finegan claims twice that efficiency.)

Noting that the unit activates only when the primary unit fails, Finegan said, "You'll see a dollar or two spike in your water bill that month."

Responding to concerns that these systems are underpowered in extreme cases, Bonifacio counters, "They work well in 90 percent of home applications."

In some jurisdictions, do-it-yourself installation of battery or water-powered systems is allowed, with permit. In others, a licensed plumber is required. Available through plumbing supply houses and Internet sites, the units retail for $295 to $500. Eldridge quotes installation in the $250 range.

To make the system work, homeowners need a minimum water pressure of 40 psi. The installation of a "check valve" for back-flow protection is a must. Both battery- and water-powered systems typically share the sump pit with the primary pump. Bonifacio noted that a water-powered backup works only when water is flowing. A water main break would likely shut it down.

Insurance Endorsement

Experts warn homeowners not to assume they are covered against losses due to sump pump failure.

"Generally speaking," said State Farm Insurance claims manager Greg Gasper, "homeowners' policies exclude water 'which enters into or overflows sump pumps.' " He said an optional endorsement provides coverage, but many decline it, learning too late that an additional $30 to $50 per year might have protected them. The endorsement typically covers loss due to sump pump failure, power interruption and a pump overwhelmed by rising water. The same endorsement also typically covers sewerage backup.

Randi Johnson, Maryland's associate commissioner for property and casualty insurance, describes the endorsement as a sound investment.

Gasper said coverage differs sharply among local jurisdictions and urged policyholders to check with their agents.

"We get these claims in the summer because of thunderstorms," he said. "But we get just as many in the winter and spring when the snow melts. The endorsement is a great purchase."