Q: I recently acquired a used 3,000-gallon steel pressure tank which I plan to use for water storage on my homestead. However, the tank has been sitting in a salvage yard for several years and is extremely dirty inside and flaked with rust. I intend to cut a hole in the tank so that I can crawl inside, clean it, and then weld it shut again. What can I use to treat or paint the inside of the tank so that it'll stay clean and be suitable for potable water? (Our water, by the way, has a pH of 5.4.)
A: First and foremost, you need to know more about the pedigree of your used 3,000-gallon tank. Was it used previously for water storage? If yes, great! If not, was it ever used to store gasoline, paint, herbicides or pesticides, industrial hazardous wastes, or other toxic materials? If so, abandon all hope of ever using it as a drinking water tank.
Second, why does your water have a pH of 5.4? This low value — indicating acidic water — doesn't fall in a danger zone, but it does make the water more corrosive to metals, so that you'd face a challenge in protecting your tank from corrosion and your water from leached metals.
A technical library, such as one at a local college, should have the information you need about protective paints and coatings. Check with the Journal of the American Water Works Association, which is published once a month and contains many leads to finding answers to your questions. The AWWA also publishes a Buyer's Guide once or twice a year along with the Journal.
Be sure to ask any of the firms you contact if the final surface will meet the standards published for water tanks by the AWWA, the EPA, and the FDA. These are important certifications!
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