Although harvesting rainwater is very satisfying, installing a complete system for all of your home’s potable water needs should be weighed against the myriad other sustainable upgrades you could invest in, like a solar water heater or an electric car. If your home is already connected to a functioning well or city water system, then it probably makes more sense to install just enough rainwater collection for your landscaping needs and keep it simple.
That said, there are renewable energy considerations involved with how you get and use water. In some situations where water needs to be pumped long distances and/or heights, like in parts of southern California and other mountainous areas, water treatment and delivery consumes the equivalent of about one-third of the average home’s electricity use to deliver water to your pipes. In situations like this, installing a whole-house rainwater system could save the energy equivalent to that produced by a multikilowatt PV system.
If you’re in a situation where access to water is in jeopardy because of drought, earthquakes, or lack of infrastructure maintenance, there are a few things to consider before proceeding. Firstly, reduce your home’s water consumption as much as you can. This means installing, at a minimum, low-flush toilets, front-loading washing machines, and low-flow shower heads (things we should all be doing anyway). Further reductions may be achieved by installing composting toilets and using greywater treatment systems for landscape watering. Fifty gallons a day per person is the most any household considering whole-house rainwater catchment should be consuming, with 35 gallons as a common goal.
Beyond your plumbing fixtures, other components of your home will make it easier—or harder—to incorporate a rainwater system. The biggest component is roofing. Prepainted metal roofing is the best material for most systems because it doesn’t leach toxins. Plus, almost all of the water is shed from the roof rather than being absorbed by the material. Tile and slate are good options (although they absorb some water). Cedar shingles work, although they collect lots of dirt and mold, and hold a lot of moisture. The most common roofing material, asphalt shingles, is generally nixed by rainwater authorities (like the Texas Rainwater Commission) because of concerns about toxins leaching out of them. Extensive studies haven’t been done (to my knowledge), so the jury is still out. Likewise, tar, treated wood shingles, copper, and gravel-based roof surfaces are out since the contaminant levels are too high. The other major concern about existing home infrastructure is older gutters that may be soldered with lead, which will need to be replaced.