In a stealth maneuver seven weeks ago, the Los Angeles County Board of Supervisors persuaded Assemblyman Chris Holden, D-Pasadena, to “gut and amend” Assembly Bill 1180, originally designed to reduce contamination from tires, to instead give them more authority to raise taxes on private property.

Publicly, the purpose is to use the new taxes to make our water supply more resilient and reduce the pollution levels in storm water heading to the ocean. Which is an important aspiration.

But the details always matter on how to achieve vital goals.

In their haste to get authority to put this tax on the November 2018 ballot, they overlooked a few important considerations.

There is no independent taxpayer oversight of the spending; there is no requirement to have an up-to-date storm water plan to spend the money; there is no assurance that the money will be used for that purpose; and there is no credit given for those who have already reduced pollution or are willing to do more to reduce pollution from their neighborhoods.

The business community and homeowners who will be writing the billions of dollars in checks to pay for this tax have asked for those basic protections. The county supervisors’ response so far is “trust us — we’ll work those details our later.” Even though there are now four new members on the Board of Supervisors, the tactics don’t seem to have changed.

We’ve been down this road before. Three years ago, the supervisors abandoned an effort to create a “rain” tax when it became clear that the property owners were going to demand an effective plan that defined the actual pathway to achieve the goals and accountability for the spending.

It will take a two-thirds “yes” vote to pass any new tax. Before we can work on making that happen, the Holden bill, describing what may be put on the ballot, must be fixed.

On Monday, Aug. 21, the California Legislature returns to finish its work before it adjourns in less than 30 days. The supervisors need to offer the taxpayers some commitments that this tax will produce real pollution reduction and enhance our water supply.

It would be a shame to miss the boat.

Michael Lewis is chairman of the Los Angeles County Business Federation (BizFed). This commentary is adapted from a letter Lewis wrote to the organization’s members.