Rainwater capture is simple in concept, and the execution is not rocket science, but there are some key points to keep in mind:

Customers should understand that a rainwater system is composed of three main parts, the “catchment” or roof that is supplying the runoff, the filters and the storage tanks. says Jack Schultz, an engineer in Santa Clara, Calif., and representative for the American Rainwater Catchment Systems Association (ARCSA).

Most importantly, they should consider every material that will come into contact with their water along that progression from catchment to filtration to storage, bearing in mind that even if they’re not planning to drink the water, they may someday want to add that function. The storage tanks and components can be plastic or metal, such as galvanized steel, which tends to be a bit more expensive, but also more durable. (And with all the recent news about toxins in plastics, it would be wise to find out what type of plastic is being used.)

Filters come in varied forms, depending on the water’s intended use and can include screens to winnow particulate matter, all the way up to state-of-the-art ultraviolet light filters that can kill bacteria and viruses, making the water safe to drink, Schultz said. A rainwater catchment expert can discuss the best filter for the system under consideration, the best materials for a given budget and the most appropriate placement plan for the site, he said.

One critical matter that must be discussed early on is the composition of the roof. The roofing materials most compatible with rainwater collection are metal (with no zinc oxide) and tile. Unfortunately, most roofs are comprised of asphalt shingles, which shed hydrocarbons into the water. The dirty run off from asphalt shingle roofs does not pose much problem for irrigation water, but would require more extensive filtration if it were used for bathing or converted to potable water, Schultz said.

So if the rainwater system is part of a new construction project, the owner would do well to consider a cleaner metal roof, some of which also offer reflective properties that help keep cooling costs down.

Many homeowners start out thinking they’ll just use the water for certain limited purposes, Schultz says, but often later on they want to expand the system’s uses, which is why the roofing material is an important early consideration.

While the rain catchment professional is assessing the house and lot, it’s a good time for the homeowner to run the project past their city building code office. Catchment systems generally are allowed, but placement might be restricted, said Greg Whitfield, owner of The Rainwell in the Dallas area. Home owners also should consult their neighborhood associations because the group may not allow the tanks to be visible from the street.