It is simple, the higher the temperature of the water the fastest the laundering reaction. But how does the water get hot? Energy is consumed to bring the temperature of the water to the required level. This process costs money to most of us using electricity or gas to heat the water. This should be considered when calculating the total cost of the process. The indirect environmental effect of energy consumption is also to be considered, for while it seems a small impact for an individual, consider the environmental cost when millions of user a doing their laundry with hot water, therefore consuming tons of fossil fuels.