A heat wave can reek havoc on plants if they're not properly cared for. One of the biggest dangers is not the leaves over drying, but the roots. Fortunately, there are several techniques that will help get your plants through even the toughest times of the summer.
Add several inches of mulch, such as bark or pine needles, around your plants. This will help retain as much water as possible because there will be less evaporation. Also, add mulch as soon as possible. Mulching early will help insulate soil temperatures when it is cooler.
Water in the early mornings when temperatures are coolest. Water near the base of the plant. Water slowly and give the plants a good soaking. Water every two or three days.
Move potted plants into the shade, even ones that need the sun. The heat might be drying up the roots without you knowing it. If the pots are dark in color, consider repotting them in a lighter color pot (which absorbs less heat) or set the dark pot inside another lighter pot if possible.
Use alternative sources of water if you are under a water restriction. As an example, place buckets in the shower with you and use that water to water your plants. Avoid getting soap in the water.