Ok, it's not completely simple, like turning on the outdoor faucet and letting the water do its thing. The greenhouses are about 500 feet from the nearest water faucet. Plus the house pump is small, not strong enough to drive the water that far. Nor do I have 500 foot of hose just lying around not being used. So I do something a bit different.
Right now I'm using the truck to transport water in trashcans down to the greenhouse area. Then using the portable generator, I use an electric sump pump to apply the water via hose. This works, but it takes time.
While there are lots of cons to this method, there are a couple pros. 1- I can add a liquid nutrient to the water to provide the plants with a fertilizer boost. 2- I can apply the water directly to the soil, thus keeping the foliage dry. 3- rather than "one size fits all" watering, I can apply extra water to spots that need it.
I figure that in the future I'll develop a better method. Not sure at this point what I'll do. Water storage directly in the greenhouse area? Some sort of gravity feed drip irrigation?
Before y'all run it and start doing all your garden watering with a hand held hose, be aware that almost all gardeners severely underwater their plants when using a hose. People think a lot more water gets into the ground than it does in truth. The easiest way to check is to use a finger to scratch the soil when your done. Visually check to see how far down the soil is wet. Your results may surprise you. In my case I know that I'm applying 100 gallons to a 100 square foot garden bed. So that's 1 gallon per square foot. I've already tested the soil and found that it wets the soil deep enough to satisfy both me and the plants.
One more note...... I never let the soil completely dry out. I apply water while it is still a bit moist. The reason being, dry soil on my farm is very difficult to re-wet. The water runs through it in channels, leaving behind 95% dry soil. If the soil is damp, then it takes the water with no problem.