Okay, the easy answer is to water your garden when there is no water coming out of the sky. However, in sever drought situations there can be water rationing rules and laws that apply during that time that don’t apply when water is plentiful. This means that it’s not only important to water on the days that your property falls on but also watering very early in the morning or in the evening can also help your garden flourish.
There is another somewhat unproven thing you can do that my grandfather practiced when water was short. He would pick the crop a few days early and let them ripen in the house instead of on the vine. His reasoning made sense to me then and still does today though I cannot prove it scientifically. He believed that by taking as much from the plant as early as possible without damage to the vegetable or fruit, it would have more to give to what was left on the stem or vine. You can try it and see what you think.
If it is forecast and you know there will be little water in the growing season, seek out plants and hybrid plants that are hearty in arid or drought prone areas. Science is working very hard to find ways of producing seeds and plants that can thrive on less water thus reducing the amount of water your garden will need over the season. You can check with your extension program at the nearest University to see if they have updated information on these types of plants or seeds for your area.
Finally, you can reduce the size of your garden and contain it in smaller areas like raised beds of pots. You might be surprised just how much you can plant in a small area.
The one thing I hope you never do is give up on your garden for any reason.