Washing Machines?

Under the sink in my flat there is only one tap to attach the hot & cold pipes for the washing machine. Not wishing to have another tap fitted I have been told that I can use a 'Y piece' to basically attach the hot & cold pipes from the washing machine to the cold water supply. If I use this Y piece what effect will this have on the temperature of the hottest washes in the washing machine. Will it simply just take longer to get up to the hottest tempearures as cold water is going in to the washing machine initially or what?