That depends on a lot of factors. If the fruit trees are well established, than they can survive with less water (but no water in summer exerts stress on the tree and might equal less successful fruiting).
Mulch helps retain water but could be more expensive than watering, unless you have a source for it (such as perhaps church members with a wood chipper and thus free wood chips).
Watering under the surface helps prevent evaporation of any water that is used, but obviously irrigation lines would be another expensive option. For free, you could use 2 liter bottles with small holes in them as a makeshift olla (the traditional ones are terracotta and I’ve heard of using clay terra-cotta pots with the drain hole plugged fully and the saucer placed over the top as an olla). This puts any water at root level.
Deep watering less often is more effective and can use less water than frequent shallow watering.
There are also plants that will be more or less effective in a xeriscape scenario, so choosing varieties that are tolerant of less water would be important.
All that aside, in the PNW if they have plenty of planting space, potatoes grow a lot of food per plant. They do need to have sort of an even amount of moisture to avoid growth problems (true of all root veg as far as I know).
Shade cloth might help reduce plant stress in the hottest parts of summer, but again it might out cost water.
I would suggest searching for xeriscape info, I don’t have a lot to offer.
Hugelkultur will sponge up water in the wet season and keep it stored in the soil for an extended period without watering. There is a lot of information available about it, but for a large scale plot, it would take a lot of wood, compost and effort. I have heard fruit trees grown on a hugelkultur berm can go without additional water.
Newly planted fruit trees need frequent watering their first year to put out good roots and are unlikely to bear fruit in a helpful time frame.
Sorry for the mish-mash list of thoughts, hope some of it helps.
