Wash water and runoff
What happens when it rains?
A reliable layout clearly separates wash mode, first-flush capture and clean-rain bypass conditions.
01
Dry period
The exposed surface accumulates sediment and operational residues.
02
First rainfall
Initial runoff is directed to the nominated storage or treatment route.
03
Volume reached
The system changes state after the design capture condition is met.
04
Clean runoff
Later rainfall follows the approved clean-stormwater pathway where permitted.
Information needed
First flush sizing and layout inputs
These details let us size the equipment and identify questions that should be resolved before pricing or construction.
- Exposed catchment area and surface falls
- Local rainfall design criteria
- Available pit, tank and plant space
- Likely pollutants and solids loading
- Wash-mode drainage arrangement
- Downstream treatment, reuse or disposal destination
Compare options
First flush or demand-driven diversion?
First flush responds to rainfall across an exposed catchment. Demand-driven systems switch pathways around active washdown. Some sites need one; complex sites may need both functions coordinated.
| Approach | Best fit | Delivery | Commitment |
|---|---|---|---|
| First flush | Rainfall on exposed surfaces | Rain event and capture volume | Unroofed bays |
| Demand driven | Active vehicle washdown | Wash operation or controls | Regular wash areas |
| Combined strategy | Mixed rainfall and wash modes | Project control sequence | Complex sites |
How we scope and quote
From site details to a quoted wash bay setup
- Send the job detailsVehicles, wash activity, location, photos and water destination.
- We check the wash area and water pathContainment, collection, treatment and routing are reviewed together.
- We price the right equipmentEquipment, options, exclusions and the next information required.
Questions we are regularly asked
Before you request pricing
Final suitability and regulatory requirements remain specific to the site, water authority and proposed discharge or reuse pathway.
What does first flush mean?
It is the initial runoff from a rain event, which can carry a higher concentration of pollutants accumulated on an exposed surface.
How much water must be captured?
The design volume depends on catchment area, rainfall criteria, site conditions and authority requirements. It should not be selected from tank size alone.
Does first flush treat the water?
No. Diversion controls where water goes. Captured water may still require settling, oil separation, filtration, reuse treatment or approved disposal.
Can the system be retrofitted?
Often yes, but existing levels, drainage access, available storage and the clean-stormwater connection need to be surveyed first.