SAFE drinking water roofs

We live in a Bioshelter that collects rainwater from 2 roof drains and runs it through our solarium sand/gravel filter before it goes into the cisten. Check it out here: https://alaskanecoescapepermaculturecenter.wordpress.com

It was built and got a national award in 1985/87. We bought it in 2008 and this summer the roof started leaking. After much research, we found what the builder originally put on the roof for safe drinking water. Here's the link: http://www.cimindustries.com/products/cim-product/cim-1061/

It's spendy, but when it comes to safe water..... gotta have it.