Loads of sympathy, well used to incompetance of a certain utility company. Make sure you claim the (paltry) compensation you're entitled to, this comes from the OFWAT site:
Unplanned interruptions
If there is an unplanned interruption to the supply, due to a burst main for example, the company must restore the supply within 12 hours unless the burst or leak is in a "strategic main" in which case the company has up to 48 hours. A "strategic main" is a major water main, which supplies the area. In addition to these guaranteed standards, companies must also, as soon as possible, take all reasonable steps to inform customers:
where an alternative supply may be obtained;
the time it proposes to restore the supply;
a telephone number where the customer can obtain more information.
If the supply is not restored within the time(s) given above, household customers are entitled to a compensation payment of £20 plus a further £10 for each 24-hour period the supply remains unrestored. Non-household customers are entitled to £50 plus a further £25 for each 24-hour period the supply remains unrestored