Downstreaming
Downstreaming is the technique of injecting soap or cleaning solution into the pressure washer's water line on the low-pressure side of the pump — downstream from the pump, hence the name. A chemical injector pulls detergent from a bucket through a siphon hose whenever a low-pressure (soap) nozzle is attached. When the technician swaps to a high-pressure nozzle, the injector automatically stops drawing chemical, allowing for a clean rinse without switching lines.
In depth
Downstreaming is the cleanest, safest chemical-application method for exterior cleaning because the pump never touches the cleaning solution — pumps are expensive and hate bleach. The technique dilutes the concentrated mix at roughly a 10:1 ratio on the way out, so a 12.5% sodium hypochlorite solution hits the surface at roughly 1-2% — strong enough to kill organic growth but gentle enough to protect landscaping when properly pre-soaked and rinsed.
How this shows up on our jobs
Every house wash, soft wash, and roof cleaning we perform in Madison uses downstreaming to deliver detergent. It is the industry standard and what separates professional exterior cleaners from pressure-washing hobbyists.
Services where this matters
Related terms
Soft Wash
Soft washing is a low-pressure exterior cleaning method that uses biodegradable detergents and a controlled bleach solution to kill the algae, mold, mildew, and bacteria that cause staining — rather than scouring them off with brute force. A soft wash rig delivers cleaning fluid at roughly 60-200 PSI, comparable to a strong garden hose, which is safe on siding, shingles, painted surfaces, screens, and caulking. The chemistry does the work: the solution dwells on the surface, breaks down the organic growth at the cell level, and is then rinsed clean with fresh water.
Sodium Hypochlorite
Sodium hypochlorite (NaOCl) is the active ingredient in household bleach and the primary disinfectant used in professional soft washing. It is sold to exterior cleaners in 12.5% concentration (commonly called "SH" or "pool shock"), roughly twice the strength of consumer bleach. When applied in a properly mixed soft-wash solution, it kills algae, mold, mildew, lichen, and bacteria at the cellular level within minutes and breaks down into salt water and oxygen.
Surfactant
A surfactant (short for "surface-active agent") is a chemical compound that lowers the surface tension of water so it can wet, spread, penetrate, and cling to a dirty surface instead of beading up and running off. In exterior cleaning, surfactants are blended with sodium hypochlorite and water to let the mix "stick" to vertical surfaces long enough for the bleach to kill organic growth at depth.
Chem Ratio
Chem ratio refers to the final dilution of cleaning chemistry at the surface — the percentage of active ingredient after the downstream injector, surfactant, and rinse water have all combined. For soft-wash work, the target ratio at the surface is typically 1-2% sodium hypochlorite for siding and 2-4% for roofs, down from a 12.5% concentrate in the bucket. Achieving the right ratio depends on injector flow rate, hose length, nozzle size, and pump pressure — and it is rarely a fixed number across all rigs.
Soap Distance
Soap distance is the maximum height or horizontal reach at which a pressure-washer rig can project cleaning solution through a low-pressure soap nozzle. It is a direct function of GPM, pump pressure, hose diameter, and nozzle orifice size — and it is the single best real-world benchmark for whether a rig can wash a two- or three-story home from the ground without ladders. A consumer pressure washer can project soap maybe 8-10 feet. A professional 5.5 GPM rig projects 20-25 feet. An 8 GPM commercial rig projects 35-40 feet with the right wand and tip.