You can also try an African style keyhole garden. It was designed for use in Africa in places where water was scarce. The garden is a 6 foot circle with the walls made up of bricks or stone or whatever is available. In Africa they would make a basket out of sticks and vines because that is what they have, but here the basket can be made of wire and it will last longer. The central basket is also your compost bin as well as where you put the reclaimed water. The rest of the circle is pretty much a lasagna garden made up of layers of straw, compost, dirt, and manure. The six foot diameter is about how much area the basket can nourish with compost and water. You would toss your kitchen scraps and also the reclaimed water from the house into the basket and that willl percolate out into the rest of the keyhole garden. When it is hot, a cover is placed on top of the basket to keep it from drying out.
Water that I have reclaimed from the house. Save the water from the shower, while you are waiting for it to heat up. I use bath and sink water to flush the toilet.
For the garden. I use the kitchen rinse water. I used to run the washing machine water outside, but the soap residue actually created an impermeable layer of soap scum on the ground so, it is not a good idea to use the wash cycle water.
To make the rain barrel water go farther. I dunk the potted plants in a five gallon bucket rather than pour the water over them. I can get up to 40 orchids watered with 10 gallons of water.
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Happy gardening in Hawaii. Gardens are where people grow.