There are portable and inexpensive small RO systems. Heck, I use one myself. What I do is fill a 35 gallon Rubbermaid can with RO water. Takes ~6 hours to fill. Don't forget to use cold water for the filter so it doesn't break. Over 3 times the water is lost or filtered leaving 1/3 pure RO water 0.00 ppm solids - using a TDS meter. Buying one is suggested. An RO buddy is an example < $200. The full 35 gallons will last me several months as I have 1 x 30 gallon tank I'm using to grow N. Ampullaria, as of last week, for the second Ampullaria growing time. Anyway I killed some moss from overheating my enclosure but it's back to normal now. If you are using it similarly to me, the use is min. so it will last years. I have the same filter - 0.00 parts per million, for over 3 years, now. Lasts but you need to figure out how to safely maintain it. It could be destroyed, the filter with little care applied. RO buddy, is inexpensive for a RO system.