Pretreat heavily soiled articles to save water. Cycles available on some machines include the super-wash cycle which adds wash cycle time, drains out half the wash water, and refills with clean hot water. When the pre-soak time is up, the tub is drained and refilled with water and regular detergent. Wrap hot water pipes to prevent heat loss between the water heater and the washer. Measure the temperature of the water after the tub has filled.
Detergents clean better in hotter water.
Water temperature also affects the solubility of detergents, especially granular, nonphosphate, carbonate detergents. When using lower wash temperatures, dissolve powdered detergents in hot water before resetting the temperature selector. Hot water is best for removing oily and greasy soil, but there are reasons for using warm or cold water. These include color preservation, fiber content, and finishes such as permanent press. Warm water can be substituted for hot water if you are willing to pretreat soiled areas such as collars, cuffs, and underarms of shirts and blouses.