Grey Water Discharge Regulation for Ships
Grey water from ships is outside MARPOL unless mixed with sewage; national rules in Alaska, in Canada and under the US VIDA regulate it in their own waters.
Grey water, the drainage from showers, wash basins, galleys and laundries, is not sewage under MARPOL Annex IV Regulation 1.3 unless it is mixed with toilet, medical-premises or animal-space drainage. No IMO instrument sets a discharge limit for grey water on its own, so the rules that apply are national or regional.
The full article will compare the national regimes: the US federal rules for cruise vessels in Alaskan waters under 33 CFR 159 Subpart E, the US Vessel Incidental Discharge Act standards, Canada’s 2023 interim order for cruise ships, flag-State guidance on combined grey water and sewage tanks, and the treatment technology that brings mixed streams under the MEPC.227(64) standard.