Water catchment tanks featured in this photo. As are shown in other gallery images, these three, 3000 gallon tanks will serve as the main holding tanks for roof catchment. Research shows us that this brand of highly stable material is the least likely to leech any unwanted toxins into catchment water. We have not created any ferro-cement cisterns that function long term in ways that we like, so have opted for these for most projects and have them ourselves for our home. When buried a few feet in the ground, they keep water from freezing in the winter.