Maybe it was coincidence that the music playing for callers holding on the St. Mary's County Metropolitan Commission's telephone line was "Hot Time, Summer in the City" just as the heat index in Southern Maryland swelled to 105 degrees for the third consecutive day, baking the region and breaking records.

Inside the office on Tuesday, commission director Steven L. King was drafting a public service announcement urging area residents to continue the voluntary water conservation efforts they started during the last heat wave in early June.

King also has been fielding calls from people who had no water because their private wells had gone dry, as water levels drop in a drought now compounded at least temporarily by extreme heat. For some, pumps can't go any deeper, so they add their names to the six- to 10-week waiting list of people who will shell out nearly $8,000 to drillers for a new well.

In the meantime, King's office is renting out 300-gallon water tanks for about $300, plus monthly charges. "That's not our normal role, but there isn't any other organization that can help these people," King said. "It's bad enough if you have to wait a couple of days, but can you imagine not having water for six weeks?"

The state of Maryland issued a heat alert on Tuesday, advising people to drink plenty of water to avoid dehydration; to wear loose-fitting, light-colored clothing; to check with doctors to determine whether certain medications -- especially diuretics and antidepressants -- could be harmful when combined with high temperatures; and never to leave children or pets in cars, even with the windows down.

For the first time this summer, Calvert County opened three cooling centers where overheated residents can get relief through air conditioning and cold drinks. The cooling sites -- at Calvert Pines Senior Center in Prince Frederick, the Northeast Community Center in Chesapeake Beach and Southern Community Center in Lusby -- are open from 1 to 7 p.m., with public transportation available. Those needing assistance to get to one of the centers can call the Health Department at 410-535-5400.

The Southern Maryland Electric Cooperative, which supplies power to nearly all of the area, also responded to the sweltering weather. Mark Volland, SMECO communications specialist, said power usage reached an all-time peak, toppling the previous record set during the winter of 1994.

SMECO distributed a set of tips to help customers avoid power shortages. The guidelines include using fans instead of air conditioning and waiting until cooler evening hours before operating large appliances such as washing machines, dryers and dishwashers.

The two most common hot-weather health risks are heatstroke and heat exhaustion, said Mary Novotny, health education coordinator for the St. Mary's County Health Department.

About 10 people a day have been treated for heat-related symptoms since the beginning of the long Fourth of July weekend, said Wesley Page, an emergency room physician at St. Mary's Hospital in Leonardtown. At Calvert Memorial Hospital, at least six patients have been treated for heat exhaustion and related illnesses since Sunday, said spokeswoman Judy Lundmark. A spokeswoman for Civista Medical Center in Charles County said the hospital had no heat-related cases.

Victims of heatstroke, which occurs when body temperature increases, can experience dry, red skin, disorientation and delirium. People with such symptoms need immediate medical attention, Novotny said. People suffering from heat exhaustion get headaches, feel weak and experience muscle cramps and nausea. They are advised to rest in cool, shaded areas and drink lots of water.

CAPTION: After several days of sweltering heat, the Lancaster Neighborhood Association pool has grown tepid, but it still refreshes Tera Foster, of Waldorf, and her 16-month-old son, Jaron.

CAPTION: Brianna Kulik, 4, of Waldorf, cools off headfirst in the Lancaster Neighborhood Association pool.