Watering vegetable garden in a drought

I water my vegetable garden as little as I can get away with commensurate with keeping things alive. Obviously I water late at night, but am wondering if it is best to water the roots or just the leaves? I am basically getting the plants to mark time until we get rain, if ever.
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
The alternative is permaculture, use perennial rather than annual veg (deeper roots) and ground cover plants to suppress evaporation (and weeds)