What is the best roofing choice for a residential rainwater collection system? Metal is most often recommended because it’s impervious, particulate-free, and easily cleaned. However, the choice of roofing also depends on the intended end-use of the water that runs off the roof surface, the slope/geometry of the roof, and the budget.
If the end-use includes potable drinking water, then the roofing material should not decrease the water quality. Metal is considered a good choice, but if the roof pitch is relatively steep, then a composition shingle (the most typical residential roofing product) is probably* not going to effect the water quality since the water runs off too quickly. Some roof geometries and roof slopes are too complicated or too flat for most residential metal roofing products. Also, some older homes are simply not straight and square enough for metal panels to be used (composition shingles can “hide” a lot of discrepancies). Always, cost is an issue, and metal roofing installed correctly costs more than composition shingle roofing.
For the example pictured above, a dark green, concealed fastener 26 gauge metal roofing panel was chosen. Since snow-melt accounts for a considerable fraction of the collected precipitation, the 3:12 pitch and metal snow break store the snow until it melts. The dark green blends in with the surrounding coniferous forest.
Keep in mind, that for potable use, you are going to be investing in a high quality water filtration system anyway. A good filter will provide you and your family with the best water available.
*disclaimer! I’m applying common sense only. I’m not a chemist, nor have I personally tested water that runs off a composition shingle roof.