Here in my area of Hawaii, we have cyclic periods of rain vs drought. So ocassionally excess rain is a problem, but mostly it's the drought periods that adversely affect the farm. Over the years I've come up with methods of conserving water that work for me. And I'm still exploring new methods, trying new ideas, toying around with suggestions that people give me. As you may have gathered by now, I like to experiment and try new things.
Using mulch is a great way of conserving soil moisture. I try to maintain about two inches of mulch covering, enough to keep the sun and wind from the soil but not so much to interfere with water getting through it.
Tilling in compost, mulch, and other organic material surely helps my soil retain it's moisture. Prior to starting this soil management routine, I noticed thr my soil dried out rapidly. Rain drained through in a patchy fashion, leaving large chunks of soil bone dry even after heavy rain. I also saw that the unimproved soil seemed hydrophobic, it repelled water. It was difficult getting it wet. I no longer have that problem since improving my soil.
I've experimented with biochar. Since I make my own as a by product of cooking, I can control the particle size. Also, I don't have to pay for it, a major plus. I add the char via the compost. That is, as I make layers in the compost pile, biochar is one of the layer additives. For most of the garden areas, I prefer the char particle size to be under 1/2 inch. I screen my finished char thru a mesh made from 1/2 inch hardware cloth, so it's simple to get the preferred size. By the way, larger chunky char is used in wet boggy garden areas since I discovered that it helps with drainage and soil texture. But that's another story.
I pre-charge my biochar by soaking in urine prior to adding it to the compost. This utilizes urine as a fertilizer in an odorless fashion. Urine in a great additive to compost, in my experience. Anyway, getting back to water conservation, biochar fortified compost appears to do a better job at moisture retention than plain compost. Everytime I make a compost pile I add roughly 2% biochar, so it gradually builds up in my soil over the seasons.
When I apply water to my garden I never use overhead sprinklers. They often send water where it is not needed. A percentage of the water is lost to evaporation while it's in the air. The tradewinds here blow the water off target. Plus you need decent water pressure to run sprinklers, something that I don't have. Anyway, my garden water runs off of gravity feed, no pump needed. A better solution is a hose going to a drip or a spaghetti system. Right now I have an old drip system made from old parts that were given to me. It's not in very good shape and constantly develops leaks. But it was a good training system. I am budgeting money to make a proper drip system this summer.
I read about an ancient system using ollas, which are porous, unglazed terra cotta pots. They are still used in some places around the world. The idea is a good one. The pots are buried in the ground up to their necks. Once filled with water, they are capped with a stone. The water gradually seeps out through the porous walls. You grow you plants adjacent to the pot, and the plant develops its roots around the pot. It is said that you use 80% less water using ollas. The only problem I have is that terra cotta is expensive here in Hawaii. So I've come up with my own idea. I substitute a plastic gallon jug. Using a fine gauge needle, I puncture it in a couple of places so that water drips out very slowly. Not as slow as with terra cotta, but it's slow. I'm just now trying out this idea at the new garden on the warm , lower acre. I'll let you know how it turns out.
Another way to grow crops using less water is to grow them in non-circulating hydroponic systems. Essentially that is a jug, such as a gallon milk jug or a small trashcan, which is filled with a hydroponic fertilizer solution, and in which you are growing a plant. I tried this with lettuce and tomatoes and it works! I now grow most of my lettuce this way, not just to conserve water but to be able to keep it out of the reach of slugs. The problem is that hydroponic fertilizer is an expense. Therefore I only grow lettuce this way.
A great way of conserving water is illegal. But then, lots of gardeners are outlaws, so using grey water doesn't bother them. Grey water is that which comes from non-toilet use. That could be your shower/bathtub, kitchen sink, clothes washer. Lots of gardeners that I know divert their grey water to their flower beds, banana patches, and fruit trees. The plants seem to thrive on it just fine.
Other water conservation tactics during times of drought are taking quick showers and no baths, not washing the car, not wasting water by doing such things as hosing off the porches or giving the animals a bath, and not using water without a darn good reason.
I know of some friends who live in chronically dry areas that installed composting toilets. It's makes sense. But I live in an area with enough water, so I haven't gone to that yet. But it's something to think about.
If water is in short supply, conserving isn't the only thing you can do. Here we work off of catchment water. So an obvious option would be to expand the collection area. Right now we collect off of our house and barn roof. To date that has been sufficient. But in a pinch we could string some tarps from trees and collect more rain water. In the next town over there is a person who rolls out a tarp in their driveway during a rain, sending the water into a pond.
One other thing that we have done has been to increase our storage capacity. During one brutal drought our catchment tank got down to 6 inches of water. Almost out! So we bite the bullet and put in another catchment tank. Now during wet times both tanks get full. It's plenty to carry us through the next drought.
One other way to capture water is to use a cloud catcher. This is not an option for us since we don't live in an area that gets clouded in. But we have friends high up the mountain who routinely get socked in each night in a cloud. They don't get rain very often and so rely on a cloud catcher system to collect their water. They have a homemade system using stainless steel wires that collects anyway between 30 to 100 gallons a night. Cool!