On the Taos Plateau of northern New Mexico where I live, nature gives us about 14 inches (356 mm) of precipitation annually. Nearby areas in the warmer Española basin and Río Grande del Norte may only receive half this amount. With some exceptions, most people (typically affluent and privileged, but not always) seem to believe that the only way to have enough water for their home is to have a deep well. This is categorically false.
Rainwater catchment is a simpler, environmentally benign, ecologically balanced way to obtain water provided that this limited and precious natural gift is used thoughtfully. It is far less likely to be contaminated by heavy metals and industrial pollutants than well water. It is also frequently less costly. But don’t take my word for it . . .
Consider the words of an expert:
For example, in my desert city of Tucson, Arizona (where we get an average of 11 inches [280 mm] of annual rainfall), more water falls as rain on our city in an average year than the entire population of the city (over half a million residents) consumes of municipal water (the bulk of which is imported/pumped in at great cost from the Colorado River over 300 miles away) in a year. So, we’d typically have more free local water than we need if we’d consciously harvest it, rather than wastefully drain it away. And we don’t need any fancy equipment or large infrastructure to do so.
A typical catchment system involves collection of rainwater and snow melt from building roof surfaces (and solar panels!) into above ground or buried cisterns (think of a cistern like a water battery – its capacity is limited). Rainwater, of course, is already naturally purified having been distilled by the hydrological cycle. However, since raindrops coalesce around dust particles, they probably contain bacteria, viruses and other biological ‘stuff’ that hangs out on dirt (the same is true, of course, for well water). More recently, evidence has been accumulating that PFAS, particularly trifluoroacetic acid (TFA)1,2,3 may also contaminate rainwater. As such, various methods for filtration and purification of the collected water should probably be applied.
So the question becomes – how much purification is necessary? Necessary to meet baseline water quality standards which are typically (and alarmingly) minimal? Or, necessary to alleviate one’s anxiety about every possible contaminant? I think somewhere in between is reasonable. As a scientist, my approach would be to 1) start with a minimal, low-cost filtration-only system, then 2) test actual collected rainwater both for common contaminants (coliforms, heavy metals) and any others that concern you (TFA?), and finally 3) have a purification system designed and installed to remove identified contaminants.
Although solar design is my area of expertise, I would also be happy to work (or collaborate) with anyone on design of a suitable rainwater filtration and purification system.
1https://www.ecocenter.org/our-work/healthy-stuff-lab/detecting-pfas-air-using-rainwater-collection
3https://www.theguardian.com/environment/article/2024/aug/16/detroit-tfa-forever-chemical