Six inputs — deposit type, age, substrate, water source, prior treatments, time available — select a rung of the six-rung removal-escalation ladder. Substrate compatibility caps the recommendation for coated, tinted-film, and heritage panels; the gentlest-first principle steps the recommendation down when lower rungs have not yet been tried.
gentlest chemistry that the inputs justify
Plain water, pure water if available, or a hose-flood rinse.
30 seconds of contact while wiping with a clean cloth or squeegee.
Flood-rinse to clear, squeegee dry.
Re-inspect under raking light. If the deposit persists, advance to surfactant-soak.