From small rain barrels to massive cisterns that hold thousands of gallons, it’s easy to store excess water from a spring storm and use it later as needed. House roofs make an ideal gathering point for rain because it’s already angled to direct it into a gutter and flush it down into a storage container. If you are building a new house and you’d like to cut your water bills by keeping your lawn and garden green with reclaimed rainwater, start by building a roof designed with water capture in mind.
All covered roofs capture the water equally well, but they differ greatly in what they add to the liquid as it travels over the surface. Contaminated water is a problem even if you don’t plan to drink your rainwater. Giving your plants water high in lead or bacteria could hurt your lawn instead of helping it.
When tested, asphalt and green roofs were labeled the worst for rainwater. Both added dissolved organic carbon to the water, which forms dangerous compounds when small amounts of chlorine are added to purify the water. Asphalt shingles also crumble as they age, leaving petroleum residue and bits of bitumen in your water tank.
Sheet metal roofing is best for a number of reasons. Durable and non-reactive enamel coatings keep zinc or lead from leaching into the water that rolls over it, along with providing lower carbon levels in the gathered water. The smooth surface also speeds up runoff and remains easy to clean when birds decide to leave droppings that introduce bacteria into your water supply. Other good options include:
- Slate or concrete roof tiles.
- Rubber roofing membranes like EDPM.
- Cool roofing products coated with a reflective paint approved for use with rainwater catchment systems.
Ask About Flashing
Besides the main material used for covering the roof, you need to check the flashing your roofer intends to use on your home. Flashing is a type of sheet metal wrapped around the edges of the roof, in addition to around protrusions like vent pipes and chimneys, that prevents water from flowing in when there’s a gap in the roof covering. Aluminum and lead flashing deposit zinc and lead particles into the water, so ask for a rubber membrane product instead.
Once the rain runs off the roof, you need a gutter to catch it before it hits the ground and seeps away. Vinyl and metal gutters both do a fine job of handling rainwater if they get cleaned regularly and feature covers to keep out leaf debris and animal waste. Instead of a usual downspout, the gutters need a PVC pipe that runs to the collection tank so water gets to its destination as quickly as possible.
Don’t forget about installing a first flush system on the pipe leading from your gutters. A first flush diverter allows a number of gallons to pass through and pour out before water starts running to the tank. This has a cleaning effect on the roof and keeps any droppings, twigs, and dust gathered since the last rain from ruining your supply.
The pitch of the gutter is also very important for rainwater gathering. Allowing the water to sit in the gutter because of a lack of slope, even for a few minutes, increases the chances of contamination from airborne bacteria. Gutters generally need at least two inches of slope for every forty feet of length to flow smoothly.
Let your roofing company know that you want to capture rainwater early on and they can help you design the ultimate roof. By arranging the slope and carefully working around any unusual valleys that might interfere with the process, you’ll end up gathering as much rain as possible each season for a greener and happier landscape.