It's really really hot! Here's how to conserve water.
In hot dry weather, keep tilling the soil to a minimum, as this causes water evaporation. A bit of hoeing doesn't harm, as it is only scraping the top of the soil and paradoxically, these weather conditions make hoeing even more effective for weed control.
Mulches keep water in the soil, as well as improving the structure of the soil itself, which allows it to absorb more water. Mulch with compost, comfrey leaves or straw, depending on the style of garden you have. Wood chip or bark chippings look good underneath shrubs. For ericacious shrubs, you can mulch with pine needles.
The best time to water plants is either first thing in the morning, or last thing at night. As the air is cooler at these times, less water will be wasted via evaporation from the surface of the soil.
Give that pot more water!
Potted plants outside, particularly hanging baskets which dry in the wind, and small pots, which heat up quickly, need more water than plants in the border. Avoid metal pots for moisture loving plants, eg) box plants, as they heat up in the sun.
Keep grass longer
Your lawn can withstand less water if you mow it on a higher setting, as the roots are more protected from the heat of the sun.
Cut the bottom off a plastic bottle, take the lid off and and push the drinking end into your pot. Then you can water directly at the root level and avoid evaporation.
Right plant, right place?
You shouldn't have to regularly water ornamentals in the garden, even in summer, unless they are newly planted. Rethink your planting to reflect the observed conditions of the soil in both summer and winter, with plants naturally adapted to those conditions, and then you will be onto a winner!
A few plants for dry conditions
Sedum, Stipa tenuissima, Papava, Cistus, Geranium sanguinium 'Album', Genista, Echinops, Eryngium, Juniperus, Oenothera, Convolvulus cneorum, Osteospermum.