If anyone in Hawaii wants to make a rain barrel, this is the web address for the Board of Water Supply https://www.boardofwatersupply.com/csswe ... m?sid=2091
It contains the parts list for what you will need. You can contact Pearl City Urban Garden center on Tues and Thursdays 9 a.m.-11a.m. to make an appt to have the barrel drilled for you. (It takes a special bit).
Food grade barrels are available ask Pearl City Urban Garden Center for locations. As to cost savings. I does not save a lot of money. Each barrel will hold about 50-53 gallons of water. That's about 10 (5gal) buckets of water. I have 2 barrels in tandem. When it rains, the barrels are full and I don't need the water. (Hint one barrel fills up fast in heavy rain, so why not have 2). I use the water when it does not rain. I use it for my orchids. I can dip about 80 orchids with 10 gallons of water. If it is a long dry spell, the barrel will be emptied quickly.
Happy gardening in Hawaii. Gardens are where people grow.