Our Superstore offers one of the largest selections of RO tanks, or what is often referred to as a storage tank, on the market today. We stock only the highest of quality that are built to last for many years. The Amtrol brand is a popular choice, and we do have it in our store. Use our convenient search engine to shop for your RO water tank by gallons or price. The standard size for most drinking water systems is the 4 gallon. We do have residential and commercial sizes in stock. If you have any questions or comments, please email or call us at 1-888-30-Water.