Don't flush the toilet every time you use it - as the saying goes: "If it's yellow let it mellow; if it's brown flush it down".
Install a dual-flush toilet - then if necessary you can use short flushs for a pee and a longer flush for the rest.
Put a suitable container in your toilet cistern - this could be a brick or plastic container or so-called hippo and it will restrict the amount of water used with each flush.
Turn off the tap when you brush your teeth - a running tap uses more water than necessary.
Take a shower instead of a bath - a conventional shower (as opposed to a power shower) uses around two-thirds less water than a bath.
Don't use more water than you need to boil the kettle - if you're only making one or two cups of tea/coffee, you simply don't need to fill the kettle.
Keep a jug of water in the fridge - then, when you want really cold water, you don't have to run the tap to get it.
Don't run taps to rinse washing up - again this uses more water than you need for the task.
Use cold, waste water to wash out jars for recycling - it does the job just as well.
Only use the washing machine with a full load - even half-load programmes use more than half the water of a full load.
Only use the dishwasher with a full load - if you have to buy more dishes and utensils, then do it.
Never leave a tap dripping - if it needs a new washer, fix it.
Don't use a garden sprinkler - it uses far too much water.
Use plants that can withstand drought - Mediterranean species like lavenders, rosemary and cistus can survive with little water.
Don't overreact to a brown lawn - it will come back with rain in the autumn.
Use 'grey' water on the garden - this is old bath and washing up water (a reasonable amount of detergent will be no problem).
Collect rain water - this is most easily done with the installation of a rain butt.
Consider rainwater 'harvesting' - this is the posh version of a water butt and consists of a large tank that collects rain from the house guttering and pumps it into the home to be used for flushing the toilet.
Wash the car with a sponge and bucket - a hosepipe uses far too much water.
Consider installing a water meter - then you'll only pay for the water you actually use and having a precise measure will encourage you to economise.
Report burst pipes immediately to the local water company - then make sure the burst is fixed as soon as possible.