Water used for washing fruit and veg in,can be re used to water your plants and lawn.
If using dish water(after washing the dishes)make sure the detergent you have used isn’t going to harm your plants, don’t use dish water on edible plants.
Waste water from your shower could also be used too, placing a small bucket in the shower will catch a considerable amount of water, even during a quick shower.
In plant pots, use old newspaper and place at the bottom, soak the paper and put the plant back in. This will help to draw the roots down for water. If you just water the top or leaves then a plant can become dry.
Water at dawn and dusk, these are the coolest time of the day. You can end up killing your plants or lawn if you water during the strong sunshine. It gives the plants time to use the moisture you give them over a longer period, rather than just evaporating away.
Keep grass longer, make sure the lawnmower blades are sharp, and at a higher setting than usual.
Long grass holds in more moisture.
Cover the soil with a few cm’s of compost, mulch or bark. This slows down moisture escaping and can help keep weeds at bay too. Don’t cover too close to the base of a plant stem, it needs room to grow.