The city’s recently approved plan to hike water rates has been confusing enough. But the way officials framed the conversation may have left some customers more perplexed.

San Diegans who own single-family homes receive a bill in the mail every other month. It looks like this and lists a given customer’s two-month water usage.

But most of the discussion about the rate hike, including city literature distributed to explain the hike to residents, has focused on monthly rate increases. That means there’s a disconnect between the explanation being offered, and the actual bills that arrive in residents’ mailboxes.

The rate increases are based on a new, four-tier system that means San Diegans who use more water pay substantially more than residents who consume less water. City officials have said the goal is to encourage heavy users to cut back and fall into a lower, less-expensive tier.

But a calculator on the city’s website that aims to show city water users how the recent changes will affect them has the potential to add to the confusion about how residents will actually be affected.

Let’s take a look at that bill again.

The city measures water use in hundred cubic feet, or HCF. The bill above lists 12 HCF.

If you plug that amount into the city’s calculator, you’ll see that current $82 water bill actually appears to fall over the next two years despite the planned hike in city water rates.

That’s just not accurate.

If this San Diego resident received the same bill in January 2014, it’d be $83.22, according to figures confirmed by a deputy director in the city’s public utilities department.

The city would seek another $6.20 for the same water consumption the following January.

The calculator works with one month at a time; water users’ bills reflect two months of use. They must be aware of the difference and go through the extra step of separating the bill into individual months in order to use the calculator effectively.

Brent Eidson of the public utilities department said that calculator and other city information are based on monthly rates.

He said the city’s website could have better clarified that the calculator uses the monthly metric. (And yes, Eidson said I was the first person to ask about this.)

For that reason, the customer whose bill lists 12 HCF of water use should divide that two-month usage total in half to get a sense of what she might expect with a future bill.

So I tried out the calculator again, using that measurement and got more accurate totals, though you’ll need to multiply by two to assess the actual bill.

What’s interesting about this is that the city itself doesn’t track how much water a given user consumes every month.

City meter readers simply check that usage every other month and other city workers send out the water bills, Eidson said.

So why the focus on monthly rates?

Eidson said the city’s other water customers, for example businesses and multi-family building owners, get a water bill each month.

The owners of single-family homes, however, receive one every other month.

“We have a combination of both monthly and bi-monthly users, so we needed to be able to speak to all our customers and we thought by speaking on the monthly charge, people could understand how that works,” Eidson said.

He said the city plans to update its calculator to better clarify its focus on monthly totals.