If you turn the tap off while you're brushing your teeth you'll save about two gallons each time. And take a shower instead of a bath, that will save about 15 gallons.
According to Consumer Reports, pre-rinsing dishes does not necessarily improve a dishwasher's ability to clean them, and by skipping the pre-wash, you can save up to 20 gallons of water per dishload. If you do one load per day, that's 7,300 gallons per year. Plus you'd save the energy used to heat the additional water.
Turn the shower water off when lathering. Not only does this save water but it gets you cleaner and means you use less product as your soap/shower gel is not immediately being rinsed away with the flowing water.
It is also a good idea to invest in a water butt in your garden. You can catch rainwater to use on your plants, without depleting your water supply. Plus it has all sorts of minerals and nutrients in it. They don't cost a lot, but are very effective.
Try not to wash your dishes every time you have any, do them all at once and then you only use one bowl of water and not a few. Think about syphoning off your bath water into a water butt for using around the garden. Fill a bottle with water, keep it in the fridge then you always have cold water to drink, it saves running the tap to get the cold water through. Have showers if possible, keep plug in and syphon that water off too.
Rather than using bricks in your toilet cistern (as they can begin to disintigrate and block your drain) better to fill a couple of 500ml plastic bottles with water and drop them in.
This may sound weird but in the winter I have a hot water bottle most nights. In the morning I use the old water to water my house/garden plants.
You can also use water from boiling pasta or vegatables, just simply tip on your garden.
Here in the U.S., shower heads that have a water miser are sold. Actually, I think those are only kind sold here. I don't know if they are sold in the UK. I love it! There's a little switch on the shower head that turns the water pressure from high to low. I keep it on low to bathe, and turn it to high to rinse shampoo out of my hair!
You don't need to use water to clean your teeth. Use less toothpaste. Just start cleaning thoroughly and spit out as usual. Don't rinse at the end of cleaning either as you are spitting out the cleaning properties in the toothpaste. Rinse with a mouthwash of your choice. You will get used to it and if you think you're going to choke, have some water. Beside saving on water, your mouth will feel much fresher and cleaner afterwards.
Use glass or stainless steel utensils for storing greasy stuff. They are easier to clean and take less water than the plastic containers especially the cheaper ones
Wash your clothes using no detergent or softener at all. The agitation of the washing machine is enough to clean slightly soiled clothes and you can completely cut out the rinse cycle too. For extra freshness, add a few drops of essential oil to a little white vinegar and add to the water. Your towels will be really fluffy too. Standard fabric conditioner reduces the absorption of towels.
Put a clean, bucket in the shower with you. It will fill up while you take a shower and you can use this water in your garden. We currently have an outdoor watering ban where we live (Atlanta, GA, USA) and this tip I received from my neighbor Lucy saved my pansies!