Judge Mooney’s dissent notes the enormous cost of dealing with rainwater in urbanized areas, but the other two members of the Missouri Eastern District Court of Appeals were not moved to overturn the trial court holding that a stormwater charge was an illegal tax, not a lawful user fee. The appellate opinion is Zweig v. Metropolitan St. Louis Sewer District.
Under Missouri’s Hancock Amendment, no tax may be imposed without voter approval. Since voters (and non-voters) insist on receiving government services beyond their willingness to tax themselves, governmental units may try to dress a tax in the guise of a service charge. MSD’s monthly stormwater did not pass the “Keller test,” which comprise five criteria that the appellate court characterized (adopting the words of former Missouri Supreme Court justice John Holstein) as “so vague and manipulable that they necessarily result in repetitive litigation and are ultimately unworkable.”
Regardless, the majority for the Eastern District found that at least two of the Keller criteria were not met, since the charge is applied to MSD customers whose rainwater drains outside the MSD area and because the charge is applied without a direct relationship to the service provided. The appellate court accepted the trial court’s conclusion that gave credibility to expert testimony that indicated that there was no relationship between area of impervious surface and stormwater runoff; impervious surface area was the basis for the amount of the charge.
Ozarks Law & Economy 
That is a disappointing ruling, because the current, out-of-date sewage and stormwater systems purge untreated sewage from the STL area into the local waterways during times of stormwater flooding (the Meramec, Missouri, and I believe also the Mississippi rivers). The additional fees overturned here were, at least supposedly, being used to update the stormwater and sewage infrastructure so that this sort of pollution could be reduced or eliminated.
Thanks for writing, Chris.
Obviously, there are two competing principles:
1. There should be no tax imposed without a vote.
2. Water pollution caused by runoff should be reduced.
Unless people are willing to tax themselves to reduce water pollution, the current situation will continue and worsen.