Prime Minister Bill English says he's open to look at charging bottling companies for water but the complex question of water ownership would need to be resolved first, and that won't happen in a hurry.

Mr English said there were a lot of difficult questions to be answered before there were any changes made to whether companies are charged for water and nothing would happen before the election.

Mr English told Morning Report the government had focused on the top priority, which was raising the quality of water.