Aloha Mrs. H,

A lot of folks on our island use rain water catchment as their only source of water. Here, we don't have difficulties with freezing during the winter, so above ground "cisterns" are the standard. Basically, it's a swimming pool filled with water via a gutter from the house roof. Depending on what power supply you have will determine the pump used to get water out of it.

You get 1/2 pound of water pressure per foot of drop so if you could locate your cistern above your garden somehow, you might not need a pump.

Since you are building a barn, you could also use the water to fill the stock tank for the horses/cattle to drink out of and then pump from there for your garden. Another option might be a pond. That could be pumped from for your garden if there's enough water run off from the roof to keep a pond filled.

Considering the cost of a water catchment system, the more uses you can get out of it, the better.

Happy gardening!

Thanks for the reply. I had given up on getting any response, so I just got lazy about checking. I've been doing a fair amount of reading and net searching about the subject, and have decided on an above ground metal cistern that I will place on a concrete platform about 2-3 ft above ground level. It will be gravity fed to the garden. I managed to find a company in Texas that manufactures the cisterns, so that will make it a little easier. We're starting the barn this Fall, so I had better get to working, lol. I was amazed at how much water can be collected off a roof the size I am talking about.
Mrs H

I've been exploring the possibilities of building a cistern system too. While researching, I ran across this 58 page guide for your state...Texas Guide to Rainwater Harvesting . Enjoy.

Thanks for the link. I was surprised at the interest there seems to be in Texas for rainwater collection, but I guess it only makes sense since we have such a long dry season during the summer.
Mrs H

I have a small 500 gallon cistern off my gutter. It only gathers from 400 square feet of roof. It takes care of my little garden most of the time. I am tinkering with the idea of more roof coverage and a second reserve tank for when San Antonio get no rain for several weeks.

On my 400 square feet I get roughly

400sqft / 12 square feet

33 cubic feet of water x 7.5 feet per gallon

= 250 gallons per inch of rain on my small collection surface.