The wash water from an exhaust gas cleaning unit can be as low as pH3, so in order to avoid a negative impact on ecosystems and potential corrosion issues, the wash water can be further diluted to increase the pH level to that required under the IMO EGCS Guidelines. To reduce the energy consumed by pumps, seawater already used for cooling duties in the engine room can be mixed with the wash water before discharge.

Studies [1] have shown that the pH of wash water will readily return to that of the surrounding water. In an environmental impact assessment of a seawater scrubber conducted over 10 months [4], samples were taken directly in front of the wash water discharge from a stationary vessel in harbour at 1 to 5 m, 50 m, 350m and 700 m. Whilst samples taken from inside the ship were pH 6.2-6.5, in no sample taken after the discharge was the pH below that of the surrounding water.