Imagine if this were to happen in the private sector. You purchase an ongoing service, and month after month the bills come. You pay them.

Months later, another bill arrives and declares that all the previous bills were wrong and that you now owe a substantial additional payment. The phone lines would burn up with calls from angry customers who now were confronting an unaffordable bill.

This is, in essence, what has been happening with Oahu residents who have been dealing with revisions to their water bills, some of which had been based on estimates rather than clear meter readings. But while the public relations problem now faced by the Honolulu Board of Water Supply is not unexpected, it can’t be tolerated for much longer.

The board has embarked on a set of changes that has not been smoothly executed, to put it mildly. The semiautonomous agency has shifted to a monthly billing system, resulting in an increase in total service charges on top of the monthly usage bill.

There have been equipment issues with the metering system, too, and that has produced a high rate of bills going out based on estimated charges.

And that’s where the biggest headache emerges. The board staff, undoubtedly running behind on a lot of adjustment chores, have hit many of its customers with revised bills. Some of these go back six months or more, seeking additional payments that can run into the hundreds — even thousands — of dollars.

Members of the Honolulu City Council have fielded calls from angry constituents. Reasonably enough, elected leaders feel the imperative to respond. Previous initiatives have sought a Council takeover of the water agency — an unworkable idea that was withdrawn — and a city audit, which the water board officials themselves find reasonable.

Now Councilwoman Kym Pine has proposed a charter amendment that would be put to a vote at the next election, effectively barring the practice of sending out bill adjustments to correct bad estimates.

Amendments to county charters or state constitutions should not be the first course of action in correcting what is essentially bad business practices by a government agency.

As written, the resolution sets an especially tough rule for the water board by disallowing all retroactive billing adjustments. Pine’s staff modeled its proposal on the practice in other states, such as California, where the public utilities commission bars retroactive billing going back more than three months.

Having Honolulu enact such a hard-line restriction in the charter would make it difficult to lower the bar somewhat should unforeseen circumstances make a more relaxed policy necessary. The amendment couldn’t be undone without another charter vote, during another election year.

The better cure for the problem is action by the water board itself, prohibiting the practice of issuing retroactive claims beyond a month or two. Further, the board seemingly has no clear recourse for consumers who want to challenge billing. There should be a formal appeals process, something beyond telling residents to call customer service lines that, more often than not, have been swamped and unavailable.

If nothing else, a charter amendment should remain as an option to pressure the water board to straighten out its operations.

Honolulu’s water board was set up with a measure of independence enabling a more professional, businesslike enterprise. However, there is little about its billing practice or its response to consumer complaints that has been businesslike or professional. The water board’s self-imposed problems need to be resolved — one way or another.