To save water and money on energy bills, many people choose to change their bath towels every week (four to seven days). The typical washing machine uses .26 kilowatts per hour of energy and anywhere between 12 to 40 gallons of water per load, with front-loading machines using less than top-loading ones. Washing your towels more frequently than once a week is very costly and environmentally inefficient. (see Reference 1)

On the Other: Wash Every Day

Others choose to change their bath towels every day or every other day, the same as is done at many hotels. This is because mildew and bacteria can form on towels when they are allowed to retain moisture for several days. Mildew can cause skin rashes and irritation. So the choice to change towels every day is an issue of sanitary preference.

Bottom Line

Because of environmental concerns, washing your towels every day is not a preferred solution to a possible mildew problem. Instead, you can take extra measures toward assuring that your towels dry completely after each use. Place the towels to hang in a well ventilated-room with the window open. Wash your towels every four to seven days or when they start to have an unpleasant odor. If you must wash your towels more frequently, purchase an energy efficient front-loading washing machine.

Source:

Saving Electricity; How to save money on the use of washing machines (clothes washers)

Livestrong; Health Risks of Mildew; Claire Taylor; 10/27/09