Does reclaimed irrigation water stain exteriors?

Start with what is not in the record: no primary source read for this answer says reclaimed water stains a roof, a paver or a window, the outside surfaces that exterior cleaning takes in.

The Florida Department of Environmental Protection names Chapter 62-610, Florida Administrative Code, as the home of its reuse rule requirements and says those rules “govern reuse and land application in Florida”; FDEP places the treatment and disinfection requirements in Rules 62-600.530 and 62-600.440. Nothing in that material addresses stains on a private exterior surface, and neither set of rules is described as regulating spotting or sprinkler overspray onto a driveway.

UF/IFAS defines reclaimed water, also called recycled or reuse water, as “former domestic wastewater that has been disinfected and treated to remove solids and certain impurities”; after treatment it may be piped back into communities for reuse, including watering lawns and landscapes, and in Florida it cannot be used for drinking.

UF/IFAS writes that reclaimed water “is highly treated and disinfected but still contains some constituents at levels outside the desirable range for drinking water,” and that it “may have higher levels of salts, nutrients (nitrogen and phosphorus), and pathogens (e.g., bacteria and viruses).” A second UF/IFAS bulletin is more specific: “All reclaimed waters contain dissolved mineral salts, for example, calcium carbonate, sodium chloride, calcium sulfate, among others,” salts that come from the original potable water and from its use.

USGS writes that “hard water is high in dissolved minerals, largely calcium and magnesium,” and calls the spots or film on dishwasher glassware hard-water residue, “not dangerous, but unsightly.” That is a glassware example, not a finding about reclaimed water or an exterior. What joins the two is general: water that dries on a surface leaves behind what it carried. No source read names a color, a stain chemistry or a removal method specific to reclaimed water.

The glossary defines hard water and the mineral deposit on their own pages.

UF/IFAS's own instructions say reclaimed water is not meant to land on hard surfaces.

UF/IFAS tells homeowners to “avoid spraying reclaimed water onto impervious surfaces such as roads, driveways, and sidewalks,” because the water then enters the stormwater system, raises nutrient loads to ponds and streams and increases plant and algal growth. It also advises minimizing overhead sprinkler irrigation so that high-salt water does not contact plant foliage, and writes that “many municipalities have few timing or quantity restrictions on using reclaimed water for irrigation” and that over-watering with reclaimed water is a common problem. How a system's heads are set is the homeowner's or an irrigation contractor's call.

Sprinkler water on glass has its own answer, why sprinklers spot windows, and NGA's rule against letting water remain on glass is quoted in the coast section of the window cleaning page. What a particular supply carries is the provider's data, not something a page can read off a spot, and salt near the coast comes up again in the salt air answer.