When I was introduced to the pond/waterfall/rock making industry, PVC liner was material that was used to waterproof our free-form ponds. It was available in 10 to 60 mil thickness, and we used 20 and 30 mil most often. We would excavate the site, install our plumbing lines, fine grade the site, install the liner and place concrete over the liner at anywhere from three to five inches thick. When I went into business for myself, I investigated other types of pond building materials and construction methods. I began using EPDM rubber as an alternative to PVC because I discovered that the PVC liner became brittle over time and was it difficult to add a patch during repair work. The Rubber liner I use is available in 45 mil thickness. There are many types of liners available made from various materials for a wide variety of uses and applications: Polypropylene, PVC, Hypalon, HDPE, LLDPE. reinforced polyethylene and even geosynthetic clay. I’m sure each has it’s pros and cons, but for the ease of installation and accessibility I prefer the rubber liner. Here are a couple pictures of liner installations:
