As far as water supplies goes, New Zealand is sitting pretty, the Saudi Arabia of water no less (especially for the early part of this summer). With such an abundance of the stuff it's a real surprise that when it is dry we have to spend so much money watering the garden. A dry summer can see your water bill jump by a third. Last year we installed a small tank, which is excellent and really takes the sting out of the water bill but we could really do with another.
How we water is becoming increasingly important. For large gardens such as my own, a sprinkler that delivers heavy droplets is really effective for intensively cropped areas and is easily adapted to the changing shape of the vege garden, but hosing gives you a more efficient use of water.
Getting out with the hose and watering each plant or group of plants according to their needs makes the most sense. This kind of watering encourages a deep root system in the plant because the water is not a thin film that just sits on top but a steady stream, which really penetrates the surface. Deep root systems in your plants are important because moisture loss is much less of a problem in deeper soil structures. Plants with deep root systems are more resilient to variations in surface moisture and can go for longer periods without some liquid intervention.
If the ground is really dry, mix a few tablespoons of garden-friendly dishwashing liquid in a bucket of water and pour that on the ground with a watering can before you water with the hose. The soapy water will penetrate a dry, hard soil much more effectively than tap water. When you follow this up with a good hosing the water will seep further into the ground.
Another benefit of hose watering is you tend to focus the water on to the ground around the plant where it's needed, so you become more familiar with your plants, so if problems arise you can deal with them promptly.
Irrigation is a really effective way of delivering regular water, although I don't use it in my vege garden. However, if I had raised planters I most certainly would. I've found the best irrigation systems are those that are easy to move about, because as plants grow they can often cast an irrigation shadow meaning smaller plants in the lea of larger ones will miss out. Individual drippers for each plant are excellent in a landscape garden.
With a water timer, drippers deliver steady amounts of water to the plant. Watering is essential to keep the garden at its best through summer but at the end of the day you're just topping up any rain you get. Remember, it's best to keep the water in the ground in the first place and the best way to do that is with mulch.