When a disaster strikes, the importance of eating smart and staying well hydrated is suddenly magnified. Under normal conditions, eating well is a way to optimize health. But a disaster changes the focus from how to eat when food is plentiful to what is necessary to survive.

Does Hurricane Katrina offer any lessons about what supplies of food and water should be stocked at home in case of natural or man-made disaster? Here's what experts advise:

Make potable water a top priority. As Hurricane Katrina demonstrated so vividly, water may be in short supply following a disaster. Drinking just a quart of water a day "will allow you to survive, although not very comfortably," said Michael Sawka, director of the U.S. Army Research Institute of Environmental Medicine in Natick, Mass.

Ideally, healthy men need nearly four quarts of water daily, women nearly three. But World War II military studies showed that troops stuck in the desert could survive on as little as a quart a day for about a week.

Water-filled foods and, of course, other beverages can be alternatives to water. "No one source [of liquid] is essential for normal physiological function and health," concludes a report on water issued by the Institute of Medicine in 2004. So canned fruit and vegetables, canned tuna in water and such beverages as juice, coffee, tea, milk, sports drinks and sodas can sustain you. Other options: fresh produce, if you can get it. Frozen fruit, juice and vegetables will likely be good for a day or two after the electricity goes off, provided your freezer stays closed.

If you're stocking provisions in case of disaster, experts say to figure on a minimum of a quart of water per person per day, or three quarts per person for more comfort. That works out to up to three gallons per day for a family of four, or 21 gallons for a week. If you don't have time before a disaster to get enough bottled water, fill bathtubs and sinks with water.

For about $75, you can buy a water purifier that removes nearly all water-borne bacteria and viruses. Germicidal tablets run about 10 cents apiece and will purify water of many types of water-borne bacteria. The tablets give the water an unpleasant taste and the treated water may still look bad. Most purifiers and tablets are not designed to remove chemical contaminants.

Don't worry about starving. That's because "you can go weeks without food" if you have water, notes Scott Montain, a research physiologist at the Army Research Institute, "although you might not feel very happy. . . . When you're stranded with nothing to do, it just amplifies the psychological burden."

Even as little as 600 to 800 calories daily can sustain a minimal level of health for a very long time for most healthy adults. But for the very young, the elderly and those with such health problems as kidney disease, diabetes, heart problems, cancer and high blood pressure, a lack of food coupled with a sudden halt in medicine and medical treatment can tip the balance in these very vulnerable groups and produce such complications as irregular heartbeats, stroke, heart attack, coma and death.

Return to basics. Most disasters knock down power lines, making refrigeration and cooking unlikely. "Avoid any foods that can spoil," Sawka said.

But there are plenty of nutritious, good-tasting foods that don't require either refrigeration or cooking. Top of the list: peanut butter. Go for the unsalted or lightly salted so as not to get too much sodium, which is likely to increase thirst.

Other good choices include tinned crackers; jerky (beef or turkey); dried fruit and vegetables; shelf-stable pasteurized cheese such as Velveeta and canned Parmesan. "They'll last up to a year or more," said Dean Sommer, a cheese researcher at the University of Wisconsin's Center for Dairy Research in Madison. Unlike other cheese, even after opening, these cheeses "will still be fine to eat" without refrigeration, Sommer said.

Nuts, chocolate, trail mix and many energy bars also have long shelf lives and are packed with calories -- a benefit when food is scarce.

Cans of beans, jars of cooked tomato sauce, packets of tuna (no can opener required), canned fish (sardines, anchovies, kippers), vacuum-packed cooked rice and some puddings, Jello, applesauce and fruit cups, UV-irradiated milk and soup in boxes are also shelf-stable. Once opened, however, they must be eaten, refrigerated or thrown away since they can grow disease-causing bacteria.

Consider a tip from the military. Stock some meals ready to eat (MREs). There are two dozen varieties, from beef stew and chicken fajitas to vegetable manicotti. They have a shelf life of three to five years, require no water, refrigeration or heating. They provide about 1,200 calories per meal and cost about $8 each or $80 for a box of 12. Find them online or at surplus stores.

During a recent taste test, our testers gave a thumbs up -- but no stars -- to the chicken fajita with salsa, western beans, crackers and beef stew, which one tester said "rivaled Dinty Moore's." Read their detailed reviews in today's Lean Plate Club e-mail newsletter. (To subscribe to this free weekly service, go to www.leanplateclub.com and click on the subscribe button.)

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Military-style meals ready to eat, about $8, provide survival nutrition.