A great hotel can be defined by many things -- quick room service, large banquet facilities, comfortable beds.

But for some travelers, a hotel can be classified as truly great only if it meets one non-negotiable criterion: a great shower in the bathroom.

Nothing is more disappointing than discovering -- usually when you're at your most vulnerable -- that the shower in your costly hotel room barely works.

Either the water pressure is weak or the shower is somehow connected to every toilet in the building: Each time someone flushes, you alternately freeze and burn.

Though many hotels run hot and cold on this issue, there are some pleasant surprises.

The Savoy hotel in London features giant, 10-inch-diameter stainless-steel shower heads in its 200 bathrooms. The shower heads are suspended from the ceiling (not mounted on the wall), and the hotel's supplemental water pressure system pumps water through narrow-gauge pipes at 68 pounds per inch. So many visitors like the shower heads that the hotel sells them upon request.

Another refreshing shower surprise can be found at the Takaragaike Prince Hotel in Kyoto. "As many people know, the concept of bathing in Japan is different," says Eiju Oshima, vice president and general manager of the 322-room hotel. "The furo (bath) is a before-dinner ritual, a relaxing social session. The showers in the hotel were installed for our Western friends."

But the showers are more than just a small concession to American bathing habits. Shower heads are equipped with special temperature governors. You can turn the faucet until it reaches a red line, making the water temperature hot and steamy, but bearable. If you want the shower hotter, you press a small red button on the faucet.

At the Park Hyatt in Washington, a mixing valve prevents water temperature from going above 130 degrees. At the Hyatt Regency in Honolulu, a similar "balancing spool" keeps the water temperature below 130, and an antiscalding device prevents sudden temperature fluctuations if, say, a toilet is flushed.

Some older hotels, even after expensive renovations, still have a problem with water pressure. At the Intercontinental in Paris, guests in rooms above the third floor often find themselves hot and cold during early-morning showers.

"Nothing can infuriate a hotel guest as much as when his shower regulates three gallons or less per minute," says Wolfgang von Baumbach, general manager of the Plaza of the Americas hotel in Dallas. At von Baumbach's hotel, water pours out of the shower at 12 gallons per minute.

Until recently, the 49-story Sheraton Hotel in New Orleans had major water pressure problems. When the hotel's giant washing machines were used, water pressure dropped dramatically. But the problem has been solved by regulating the time and the amount of water used by the laundry.

At the old Biltmore hotel in Los Angeles, poor water pressure was the major complaint by guests. Two years ago, new owners spent more than $1 million installing new water tanks and a new boiler system. They also reduced the number of rooms from 1,100 to 707. "We were able to increase {water pressure} 65 percent," says Lee Jenks, vice president and general manager. "That'll give you an idea of how bad it was before."

Some think the worst showers are found at resort hotels, where it sometimes seems more money is spent on the outside environment than the bathrooms. The Hyatt Regency in Maui, despite special booster pumps, suffers from chronic water pressure problems. Since the hotel is the last one on its stretch of beach to get water, the pressure suffers accordingly.

But there are exceptions to the resort rule. One of the nicer hotel shower surprises can be found in southern Brittany, in the French resort city of La Baule. Dozens of little hotels line the beach facing the Atlantic, and most of them offer tiny rooms and spartan bathrooms. But the 30-room Castel Marie-Louise is exceptional: Its showers have wonderfully high water pressure, and a consistency of temperature that guarantees an invigorating wash-up -- and sheer bliss to the shower fanatic.