Pervious surface

No Florida statute or water rule among the sources behind this page defines "pervious surface". The term is used, not defined, and what it means has to be read from how the instruments use it.

The county's washing rule

Collier County 311's summary of Ordinance 2015-27 permits washing home exteriors and roofs at any hour with low-volume equipment or a hose fitted with a self-canceling nozzle, then adds: "In all cases, the water used must drain to a pervious surface or to a water recycling/reuse system." The sentence offers two destinations, and the ground is only one of them. How the whole standing rule reads is set out in the Florida rules for a roof cleaning, and the driveway side of it in the paver cleaning rules.

The district's shortage rule, for vehicles and boats

In a declared Phase I, the South Florida Water Management District's Rule 40E-21.521 says mobile equipment washing "shall be conducted over a pervious surface or in an area that immediately drains to a pervious surface", and the same line recurs in the later phases. The chapter defines mobile equipment as automobiles, trucks, trailers, railroad cars, campers, boats and similar equipment, so this line is about vehicles and boats, not buildings or roofs. The water shortage phase entry explains what a declared phase is.

A city's plainer words

Bonita Springs never uses the word in its Ordinance 21-07 water conservation summary, nor did its earlier 06-06 summary. For pressure washing it advises, "Channel runoff water onto the grass or another non-paved surface," and for a car it suggests parking "over a non-paved or porous surface to limit water runoff". Those are the city's best-practice lines for its own addresses, not a definition of the county's or the district's phrase.

UF/IFAS Extension gives the clearest account of both sides of the term. On one side, "Rainfall will often encounter impervious or pervious-resistant surfaces such as streets, parking lots, sidewalks, gravel roads or lots, rooftops, and other developed areas." On the other, it describes diverting downspouts to pervious surfaces so water can "infiltrate the soil", and calls rain gardens "pervious areas of the landscape that can soak up rainwater and prevent stormwater runoff."

Gravel shows how unsettled the edges are. The same UF/IFAS publication puts gravel roads or lots on its pervious-resistant list and also says that "Washing the automobile on gravel or grass gives the water an opportunity to be filtered before it can arrive at a storm drain, surface water body, or groundwater source." It holds both statements, and neither decides whether gravel is a pervious surface under the county's rule.

Ground that soaks water in does not close the question: FDEP's vehicle and equipment washing guidance says a grassy surface can treat only small ("minimal ponding and no runoff") and infrequent discharges, and UF/IFAS says wash water containing phosphate or cleaners that do not break down should not soak into the ground at all, if possible. How those limits sit beside a roof wash's rinse is taken up on what happens to the runoff from roof cleaning, and a shaped grassy low area built to take runoff is a swale, a separate term.