EVERYBODY has a flood story. Mine involves our hot water heater. We had just put the finishing touches on our Christmas tree, the younger kids were put to bed, and my parents, sister and I got ready to attend midnight mass.

Suddenly, our 15-year-old babysitter appeared on the porch: "Mr. 15789hing funny -- like a boom."

It wasn't something funny. It was a basement full of hot water. The water heater, also 15 years old, had burst and our basement looked like Niagara Falls. So much for going to mass. We spent the evening in boots and raincoats, bailing out buckets full of water, waiting for the plumber . . . and waiting for Santa.

"Any indication of water around your hot water heater should never be ignored," warns Kay Keating, who teaches plumbing workshops for the Washington Suburban Sanitary Commission, one of the three water suppliers for the metropolitan D.C. area.

"If you notice a puddle, turn off the shut-off valve above the heater or if you don't have a valve, shut off the water throughout the house. Then call your plumber. A slow leak can very quickly turn into a burst heater," she says.

There are problems to be on the lookout for, but the experts -- from area plumbers to heater manufacturers to the people with the electric and gas companies -- agree that hot water heaters are almost maintenance-free. The two most common recommendations:

Keep your hot water heater set at 140 degrees. A higher temperature can cause an explosion; it also isn't energy efficient. If you don't have a dishwasher, the heater can be set at 120 degrees. Dishwashers require the hotter temperature to dissolve and rinse the soap.

Your heater must be drained or flushed out periodically. How often you should do this depends on whom you ask. The best advice is to follow the care instructions that come with your heater. The model, size, age and type of heater you have -- gas, electric, oil or solar -- will determine how often you should drain or flush it. But the hardness of the water mainly determines when to clean the heater.

Moderately hard water (which is what most of the D.C. area has) leaves a mineral buildup inside your heater that needs to be cleaned out. Leaving it there makes your heater work harder and less efficiently. It also shortens the life of the heater. Softened water leaves some buildup, but not as much.

Draining means bleeding or emptying the tank of a few gallons or buckets of water -- till the water is clear. Flushing means completely draining the tank and then running cold water through it several times.

"About once a month," advises J.T. Adams in "How to Repair and Maintain Home Systems & Appliances," (Arco, 1981), "flush the sediment out by drawing several buckets of water from the tank through the faucet."

Plumbing inspector Bill Norrington of the WSSC says a once-a-month draining is necessary for both electric and gas heaters,

Frank Elliott, manager of Climate-Trane, a plumbing equipment store in Rockville, agrees: "The metal deposits build up and should be removed each month, especially with gas and oil heaters, which generate more sediment than electric heaters."

Eric Oganesoff of PEPCO says the company recommends a once-a-month draining if you have very hard water and twice-yearly if your water is soft.

Bruce Kramer, service manager of Bethesda Plumbing, on the other hand, says one good annual flushing -- if done properly -- is all that's needed. "A flushing, not just a draining of a couple of gallons a month, really cleans out the tank," says Kramer. "The valve that you drain it from is located above the bottom of the tank. By draining the tank, you're getting water at this level and above -- not from the very bottom of the tank where the sediment is."

Kramer describes how he flushes out his water heater tank:

First, turn off the cold water valve. Open up a hot water faucet upstairs -- preferably in the kitchen. This prevents the air from getting trapped in the tank. Attach a hose onto the drain at the bottom of the heater. Turn on the cold water inlet valve above the heater -- full force for about 1 1/2 minutes. The cold water shoots down the dip tube to the bottom of the tank. When it slams into the bottom, the sediment is stirred up and runs out the hose. Kramer suggests doing this three or four times.

Kay Keating agrees. The sediment never really gets stirred up with just a small bleeding, she says. She also hooks up a hose to the heater's drain and allows the tank to drain for about five minutes -- but never completely empties it. "If you do drain the entire heater," warns Keating, "make sure the tank cools off before you run the cold water through."

Plumber Steve McMichael of Flood Plumbers also recommends a once-a-year flushing for both gas and electric heaters. "Although," he notes, "a monthly draining might get rid of the sediment before it begins to settle on the bottom of the tank."

Joseph Bauer of Bauer Plumbing in the District admits that most water heater manufacturers recommend that the homeowner drain their tanks "periodically," and that "I take this to mean two or three times a year -- but no one I know does."

Efficiency tips in hot water heating:

Insulation jackets

Eric Organesoff, manager of the Residential Energy Services Department at PEPCO, suggests putting a fiberglass insulation jacket around your heater. (Do-It-Yourself insulation kits can be bought at most hardware stores for about $20.) PEPCO suggests getting R-5 insulation. Organesoff explains that a lot of heat escapes from the walls of your heater; you end up paying for heat that never reaches the water it's supposed to be heating. PEPCO estimates that an insulated electric heater can save the homeowner about $25 a year. (You only save $5 the year that you buy it, but in time it saves money,, according to PEPCO.) PEPCO also figures that electric hot water heaters cost about $240 a year to operate in this area.

Susan Butz, company spokesperson for Washington Gas and Light Company (WGL), says gas hot water heaters here cost about $138 a year to operate. With an insulation jacket, Butz estimates you can save $15.

Fixing leaky faucets

One drip a second from a leaky faucet can waste up to 60 gallons of water a week, according to WGL and PEPCO. If it's from your hot water tap, the money you've paid for heating the water is literally going down the drain.

Shower flow restrainers

WGL and PEPCO recommend shower flow restrictors. They're available at hardware stores for $2, snap onto the shower head, and cut the flow of water from six gallon per minutes to three.

Appliance use

Run dishwashers and washing machines only when full.

Buying water heaters

The new energy-efficient models have glass linings (to prevent rust) and double-thick insulated walls, says WGL's Butz. Keating recommends insulation jackets even for the new insulated heaters, as well as insulation around the pipes to maintain the water temperature.

In gas heaters, the new pilotless ignitions are nice, adds Butz. "You never have to worry about lighting the pilot light when there's a draft." She warns that if you ever do have trouble lighting the pilot, "don't fool with it. Turn off the gas controls and call a plumber or gas or heating contractor."

Water heater prices, including installation, vary: $400 for gas, $500 for electric, $800-900 for oil and $1,000 for solar. Gas and electric are still the most common, says Butz.

Washington Gas advises buying a water heater with the capacity and recovery rate you need. The recovery rate, explains plumbing inspector Norrington, is how fast your water gets hot again after you use hot water. Gas recovery is faster than electric, he says.

Problems you may encounter with a hot water heater:

First thing in the morning, you run hot water for a shower. It's hot for a few minutes and then it cools. Why?

Kay Keating says this may be caused by a dip tube that has broken off -- the tube through which the cold water enters your water heater. It should extend to the bottom of the tank. If the tube is broken off, the cold water is going right to the top of the tank without getting heated. The dip tube will need to be replacedin this case.

A gurgling sound from the heater may mean that the temperature is set too high. If you have an old gas heater, adds Keating, it may also mean that there is too much sediment on the bottom of the tank. The flame from the bottom of the tank is heating up the sediment, causing it to bubble up and produce a gurgling sound. Time for flushing out.

A snapping or hissing sound in a gas heater could mean a leaking tank. The sound comes from leaking water dripping onto the flame. Don't fool with it. Just turn off the water or shut-off valve over the heater. Then call the plumber. Keating recommends a shut-off valve when installing a new heater. "It'll save you a plumber's weekend rates, if your heater breaks down Saturday morning and you run the house on cold water till Monday."

Kay Keating's upcoming plumbing workshops:

Sept. 30 -- three-hour session for the Montgomery Department of Recreation, $4.75. Location: Bauer Drive Community Center, Rockville.

Oct. 3 -- three-hour workshop for the Gaithersburg Department of Recreation, $4.75. Location: Casey Barn, Route 355 in Gaithersburg.

Nov. 21 -- five-hour workshop at Prince George's Community College, $10. Location to be determined.