It would cost city taxpayers more than $10 billion — perhaps much more — if Albany approves a controversial gas-drilling project called hydrofracking upstate and the city has to build filtration plants in the nearby watershed, a city official testified yesterday.

“That estimate does not take into account any revised treatment technologies or additional treatment technologies that may be needed to address the specific contaminants that may result from hydraulic fracturing,” Assistant Environmental Commissioner David Warne told a City Council hearing that drew more than 200 people.

“I don’t want anyone to leave thinking that is the number.”