He declined to comment on the charges today.
The charges, under the Health and Safety in Employment Act 1992, were laid with the Auckland District Court.
No court date has been set and the Department of Labour refused to say how many each company was facing.
Neither Watercare or the Department of Labour would expand on written press releases.
Watercare said the incident happened while workers were inspecting a watermain that had been removed from service.
Chief executive Mark Ford said the company was committed to ensuring all possible lessons were learnt.
"We have always had a strong focus on workplace health and safety and prior to this incident we had an 18-month period without a single lost-time injury.
"Preliminary inquiries show that the specifics of this incident - where reticulated gas entered a drained water main - appear to be unprecedented in the water industry anywhere in the world.''
Department of Labour northern general manager John Howard said: "There are too many people dying and being injured at work and the Department is committed to bringing down this toll.
"Our investigation was very thorough and looked at whether the legal obligations were complied with, what caused the accident and what can be done to prevent this happening in the future.''
Vector, the company which supplies gas to Auckland, has not and would not be charged over the incident, said spokeswoman Sandy Hodge.
"It wasn't our worksite.''
Ms Hodge said the company only provided a gas distribution system and natural gas was not involved in the accident.
"There's been a question about [natural gas], with Mr Ford saying preliminary enquiries indicating [natural gas was involved]. That's not what our enquiries show.''
