Hot water is taken for granted and looked upon as an integral part of most American households. Little thought is given to the cost of heating water because its use is constant rather than seasonal, as with a central heating system.

The heating of water accounts for a whopping 15 per cent of your total energy bill. You can't do without hot water, but there are several ways to conserve it so that energy requirements and costs will be less.

Hot water usage depends on the number of people in a household, the number of bathrooms and on the presence and regular use of a clothes washer and-or automatic dishwasher. Water heating units, usually using gas, electricity or oil, are specified in terms of tank size, rate of heat input, maximum estimated hot water usage per hour and recovery or reheating capacity rated in gallons to keep unneeded water hot, an undersized unit cannot supply a sufficient amount of hot water. A reliable heating and plumbing contractor can determine the size tank needed in your household.

Look for information indicating how energy-efficient the unit is and how thickly insulated the outer shell is. When replacing a gas-fired unit, select one equipped with a low consumption pilot that is matched to the rate of heat loss of the heater.

Relocate the unit, if necessary, as close as possible to the area of major hot water use. Use small-diameter pipes for hot water supply lines to minimize heat loss and to reduce the volume of trapped water.

A thermostat setting of 110 to 120 degrees fahrenheit on a water heater is sufficient if you do not have an automatic dishwasher. A setting of 140 degrees is recommended if you do have one. Temperatures of more than 140 degrees shorten the life of a glass-lined tank.

Twice a year (monthly, if you live in an area with heavy mineral deposits in the water) empty a bucket of water from your unit. This will help remove sediment that separates the tank from the source of heat and wastes energy.

A leaking hot-water faucet is an enormous waster of energy and should be repaired immediately. The replacement of washers is a simple operation described in every basic homeowner's maintenance and repair guide.

A simple rule of thumb applies to energy conservation and hot water: Every time you use cold water instead of hot you save energy and dollars. The following tips will help reduce hot water consumption:

Wash only full loads of laundry. Use water-level or load-size devices on your clothes washer.

Use as low a water temperature as possible for the wash cycle of your clothes washer. Use cold water for all rinse cycles. Presoak heavily soiled clothes.