Watercare spent nearly $10,000 per day on lawyers last year.
The external legal bill for the utility, which is owned by Auckland Council, rose by nearly $1 million last year from $2.6 million to $3.5 million.
Cr Cameron Brewer said the amalgamation of the city was supposed to bring a reduction in these kind of costs and this represents a broken promise by Mayor Len Brown.
Cr Brewer said Watercare is obliged to keep operating costs down, but this increase in spending will inevitably end up being passed on to residential and business owners.
Watercare said on Wednesday that since the amalgamation of the city it's saved more than $100 million in regional cost efficiencies.
The utilty said it has $1.5 billion worth of projects underway and most of these require resource consent.
Watercare said it's required to go through the resource consent process the same as everyone else and frequently has to go before the Environment Court which means it needs specialist lawyers.