It's tough when temperatures are this hot to save water but this is when we need to most.
We've been determined not to use fresh tap water for our vegetables and have installed a number of water butts. Even then we're now running low and the forecast is not looking good, so every drop counts .
Put a bucket into the shower (avoid baths) with you and collect the water wasted whilst you wait for it to warm up and leave it in while you shower to collect the aptly-named "grey" water. I collected about half a bucket for just a quick shower.
When showering feet tend to get neglected so rather than resorting to a bath have a footbath (apologies for the pic ) and then use the even greyer water to water the plants.
Use a washing up bowl or any bowl to catch excess water when washing hands or rinsing something. Don't throw away cooking water from cooking rice, pasta or vegetables or from boiling eggs. Tip any excess water into a communal bucket that can be used to water the vegetables.
Obviously avoid using harsh chemicals so that the water can be safely used in the garden.
And whatever you do, DON'T water the grass, it will recover!