A Greymouth woman was taken to hospital on Tuesday after her former partner allegedly poured boiling water on her.
When police visited another Greymouth address to speak to a 33-year-old man in relation to the incident, they found a growing room with "a substantial amount" of cannabis, acting senior sergeant Paul Watson said.
The man was arrested for assault, breach of a protection order, cannabis cultivation, cannabis possession, unlawful possession of firearms, and unlawful possession of ammunition.