Wash your clothes at a cool and efficient 30°C and all that will shrink is your carbon footprint (oh, and your energy bills). Most modern detergents are designed to work perfectly at cooler temperatures, so you'll still get your whites sparkling.
We've all become so accustomed to having piping hot water at the twist of a tap that it's easy to forget what an energy-intensive luxury it is.
Heating water in your washing machine uses a great deal of energy: by washing your clothes at 30°C you could save 45 kgCO2 a year.1
I was pleasantly surprised how little difference there seemed to be in the wash between low temperature and a normal 40 degree wash.
Made no negative impact on my washing for a good cause :)
I try to make my washes as infrequent as possible, but when I do put a wash on I now make sure that it's on 30 every time!
Washing at 30 made no difference to the washing so I will continue to do so.