Can you use graywater or rainwater in a misting system?

No, not for misting people. Graywater (also spelled greywater: used water from showers, baths, bathroom sinks and washing machines) is wastewater in every state rule, and none of the seven state rules read for this page provides for misting with it. Three ban spraying it outright, three allow untreated graywater only below ground or by drip, and the two that allow spraying treated graywater limit it to irrigating plants: Texas only when nobody is in the area, Oregon away from food service and with written approval for anything that makes aerosols. Rainwater is a different case: collecting it is usually legal, but its safe use is watering plants, not misting a patio. This page sets out each rule, the one setup that does work, and how far a rain barrel goes.

Why do some people say graywater works in a mister?

Because the question usually gets treated as a filtration problem: will lint and hair clog the nozzles? A 5 micron cartridge does solve that. But the filter that sits in front of a high-pressure pump, described in water supply and filtration, is there to protect orifices from particles. It is not a disinfection step, and none of the rules below treats it as one.

Regulators treat graywater as wastewater first. Texas defines it as "wastewater from showers, bathtubs, handwashing lavatories," non-kitchen sinks and clothes washers. The rules then grade what may be done with it by how much contact people will have, and spraying sits at the top of that scale because a spray turns the water into droplets that drift and can be breathed in. CDC's description of Legionnaires' disease makes the same point about any water: "People can get Legionnaires' disease when they breathe in mist that contains the bacteria." A misting system is a machine for producing exactly that mist.

What do state graywater rules say about spraying?

The table collects the residential graywater rules of seven states in the West and Southwest, the region where misting and graywater reuse overlap most. Each line is from the rule text itself.

Spraying household graywater under state rules (read 2026-10-14)

State and rule	Spraying graywater	What the rule allows instead
Arizona, R18-9-D701 (under 400 gal/day)	Prohibited: no application "by a spray method"	Surface application "only by flood or drip distribution methods"; not on food plants except trees and shrubs
California, 2025 Plumbing Code 1503.1	Prohibited: graywater shall not be used in spray irrigation	Release under at least 2 in (51 mm) of mulch, rock or soil, or a solid shield; no ponding or runoff
New Mexico, 20.7.3.810 NMAC (under 250 gal/day)	Prohibited: condition reads "graywater is not sprayed"	Flower gardening, composting, landscape irrigation; not stored over 24 hours; no food plants except fruit and nut trees
Utah, R317-401	Not covered	Rule applies to graywater systems "for subsurface landscape irrigation"
Washington, WAC 246-274	Not covered	Chapter exists for "reusing greywater for subsurface irrigation"
Oregon, OAR 340-053-0090, Type 1 and 2	Not allowed	Type 1 (untreated): subsurface irrigation only. Type 2 (BOD and TSS 10 mg/L or less): adds surface drip irrigation
Oregon, Type 3 (secondary treatment plus disinfection)	Sprinkler irrigation of plants allowed	Not within 10 ft of a property line, or of "an area where food is being prepared or served"; aerosol-making decorative fixtures "only if authorized in writing"
Texas, 30 TAC 210.83 (under 400 gal/day)	Allowed only under conditions	E. coli limits, applied when people and pets are not using the area, no drift off property; uses limited to foundations, gardening, composting, landscaping and toilet flushing

Read across the rows and a single pattern holds. Untreated graywater never leaves the ground surface in a spray. Where a state does allow spraying, it is treated water, onto plants, kept away from people or food. No row allows the thing a patio misting system does, which is to put fine droplets into the air people are sitting in.

Could treated graywater ever be sprayed legally?

In Texas and Oregon, yes, but only for plants, and the bar is high. The Texas rule says graywater "shall not be applied using a spray distribution system except in accordance with" five conditions. The first is a water quality limit: E. coli "less than 14 most probable number (MPN) or colony-forming units (CFU) per 100 milliliters for 30-day geometric mean and less than 240 MPN or CFU per 100 milliliters maximum single grab sample."

To put that number in context, EPA's 2012 recommended criterion for recreational water, the standard states use to decide whether a beach is safe for swimming, is a geometric mean of 126 E. coli per 100 mL at its higher illness rate and 100 per 100 mL at its lower one. Texas's spray limit of 14 is about 9 times stricter than the higher figure. Graywater clean enough to spray in Texas has to be much cleaner than a lake you could legally swim in, which takes a treatment system and regular sampling, not a filter.

The other four Texas conditions are what close the door on cooling:

• Timing. Sprayed graywater "must be applied at times when people and pets are not actively using the distribution area." A misting system exists to be used while people are in the area.
• Weather. No spraying during rain, on frozen ground, or within 24 hours after one-half inch or more of rain.
• Rate. Applied "at a rate to prevent ponding, puddling, or runoff."
• Drift. It "must not be sprayed or allowed to drift off property." Fine mist drifts by design, which is why wind above about 5-10 mph carries it out of a patio.

Oregon reaches the same place by a different route. Its Type 3 graywater must have secondary treatment (BOD and TSS of 10 mg/L or less) and disinfection to a median of 2.2 total coliform organisms per 100 mL, with no single sample over 23, and only then may it run sprinklers on gardens, lawns, living walls and greenhouses. Patio cooling is not among the listed uses. The 10 ft setback from anywhere food is "being prepared or served" excludes the outdoor dining areas that are a common reason for patio misting, and the clause on "aerator or decorative fixtures that may generate aerosols" requires written approval from the state for anything built to make a fine spray.

Is rainwater legal to use in a misting system?

Collecting it is legal in most states, and the rules that limit it are about quantity, not misting. Colorado is the best known restriction. Its 2016 law, C.R.S. 37-96.5-103, allows rooftop collection only if:

• no more than two rain barrels with a combined capacity of 110 gallons or less are used;
• the roof is on a building used primarily as a single-family residence or a multi-family residence with four or fewer units;
• the water is "used for outdoor purposes including irrigation of lawns and gardens"; and
• it is used on the property where it was collected.

The statute does not name misting. "Outdoor purposes including" irrigation reads as a broader category than irrigation alone, but whether a patio mister counts is a question for Colorado's water officials, not one the text settles. A 2025 bill, HB25-1106, would have removed both the capacity limit and the restrictions on use; the House Energy and Environment Committee postponed it indefinitely on February 13, 2025, and its status reads Lost, so the 110 gallon limit stands.

Texas sorts rainwater into a category it calls alternative onsite water, alongside air-conditioner condensate, foundation drain water, stormwater, swimming pool backwash and drain water, and reverse osmosis reject water. Its rules require piping that carries these sources to be purple, exposed piping to be stenciled "NON-POTABLE WATER" in yellow, and note that they may be subject to backflow prevention requirements. Whatever your state, the plumbing rule is the same: an alternate supply must never connect to the house's potable piping. A tank filled from above through an air gap, as described in running a misting system from a water tank, keeps the two systems separate.

Is rainwater safe to mist over people?

Not on the evidence available. CDC says "even when rainwater looks clean, it can contain germs and chemicals that could make you sick," and names the routes: dust, smoke and other particles in the air before the rain lands, bird droppings on the roof, and metals such as lead and copper leaching from roofing, gutters, piping and storage. Its listed safe uses are to "water plants you do not eat" and to "wash items you do not use for cooking or eating."

A misting system adds two problems of its own on top of that list:

• Stored, warming water. CDC says Legionella "grows best between 77°F-113°F (25°C-45°C)" and that "slowly moving or stagnant water" gives it the opportunity. A rain barrel is stored water by definition, often for days between storms, and it sits outside through the same hot afternoons that call for misting. The site's water hygiene and Legionella guide covers flushing and disinfection for any misting supply.
• Delivery into the breathing zone. Watering a plant puts water on soil. A misting system, and a misting fan above all, puts it as fine droplets at face height, which is the exposure route CDC describes.

So the line we draw is the same as for graywater: rainwater for misting plants, potable water for misting people. That matches CDC's safe uses without stretching them, and it is the setup the propagation mist guide already assumes when it warns that holding tanks can carry pathogens onto cuttings.

Which water can go in a misting system?

The table sorts the sources people ask about by the two uses that matter.

Water sources for misting: over people vs plants only

Water source	Misting people (patio, fan)	Misting plants	Why
City water or a tested well	Yes	Yes	Potable supply; the default every pump manual assumes
Rain barrel or cistern	No	Yes, preferably not on food crops	CDC safe uses are plants you do not eat and non-food washing
Untreated graywater	No	No (drip, mulch basin or subsurface only)	Spraying banned or not provided for in all seven state rules
Treated graywater (TX spray limits, OR Type 3)	No	Only where the state allows it, under its conditions	People-present spraying excluded in Texas; food-service setback and aerosol approval in Oregon
Reverse osmosis reject water	No	Plants only, and expect scale	The concentrate carries more dissolved minerals than the tap water that fed it

Reject water deserves its own warning because people who buy reverse osmosis for spot-free misting, the choice the hard water and water treatment guide makes when spotting matters, often look for a use for the concentrate. Evaporating mist leaves every dissolved mineral behind, so the concentrate is the one water guaranteed to scale nozzles faster than what came out of the tap.

How long will a rain barrel run a misting system?

Less time than most people expect for a patio, and a long time for plants. Runtime is the stored gallons divided by total nozzle flow. The table uses Colorado's 110 gallon cap and this site's planning flows at 1,000 psi (0.008 in nozzle about 0.96 GPH, 0.012 in about 1.5 GPH) and 0.5 GPH for hose-kit nozzles, with the pump's bypass returned to the tank.

Hours of continuous misting from 110 gallons, and the rain that refills it (MistGuide calculation)

System	Water use	Hours from 110 gal
Portable fan, 5 x 0.008 in	4.8 GPH	about 23 h
Hose kit, 20 x 0.5 GPH	10 GPH	about 11 h
Patio, 16 x 0.008 in	15.4 GPH	about 7 h
Patio, 20 x 0.012 in	30 GPH	about 3.7 h

Rain barrels feed a misting pump the way any tank does, which means a booster for pumps with a low-pressure switch, a strainer on the tank outlet and the usual 5 micron filter. The water tank guide covers the plumbing in order.

When does this advice stop applying?

• States not in the table. Graywater rules differ widely and change. The seven here were read on the date shown; check your own state's environmental or plumbing agency before building anything.
• Municipal recycled water. Treated wastewater delivered by a utility through purple pipe is regulated under separate reuse rules, not the household graywater rules above. Its permitted uses are set by the utility and the state, and none were read for this page.
• Treated systems with a permit. A state permit can authorize uses the general rules do not. Oregon's aerosol clause, for example, allows aerosol fixtures with written approval.
• Livestock and commercial operations. Barn cooling and industrial dust suppression run under agricultural and occupational rules this page does not cover. For backyard birds, see misting for backyard chickens.

For everything else on the supply side, from hose bibs and backflow devices to wells and tanks, start at the installation section.