Wow, what a hot summer we have been having. You know its hot but just think about your plants. In most cases, the gardener needs to supplement natural rain water. The questions of how much and how often are a matter of judgement. The best way to tell when a garden needs watering is to look at it. If the soil is dry to a depth of a half an inch or so, it's time to water. How often you need to water varies greatly with the temperature. With high temperatures in the mid-70s (24 C), watering once a week will probably be more than adequate. But when temperatures hit the mid-90s (35 C), you may need to water as often as every other day. Other factors influencing the frequency of watering are the nature of the soil, the amount of sunlight, how well the garden is mulched and whether the plants are in flower (during flowering plants generally require more water). But always keep in mind, you can most definitely water too much.
When watering you want to make sure the soil is well moistened. This can be time consuming, but it is better to water thoroughly once a week than to give your garden a brief shower every day. Never use a spray nozzle on a hose, it delivers either too strong a flow or an inefficient mist. The best way of controlling water flow is to use your thumb. Always try to water the base of the plants, but in times of meager rainfall you can give the foliage an occasional spray as well. The best time to water is in the morning, but the warnings against mid-day watering are over done. Late evening is probably the worst time to water, as it leaves the foliage damp at night when molds and fungi are most active. But never let a bone-dry garden go without watering simply because you can't do it at the optimum time of day.
Don't give up on your plants if they are severally wilted as they are doing everything possible to just stay alive. A good long watering will do amazing things if you can provide the plants with the water necessary for them to recover.