There’s a lot to like about Mayor Jim Kenney’s proposed soda tax, which could add a projected $48 million to the city’s budget in fiscal year 2017, if adopted by City Council. Most of the money is expected to fund universal pre-K education, parks, libraries and recreation centers.

Kenney’s proposal calls for a 3-cents-per-ounce tax on all surgary drinks but would not apply to diet drinks. The tax is all but certain to be passed along to consumers and the beverage industry and its allies have suggested it will make the city less competitive. It’s also worth noting that Kenney’s predecessor in the mayor’s office, Michael Nutter, twice failed in a bid to enact a similar tax.

Only one other city in the U.S–Berkeley, Ca.–currently has imposed a similar tax, although it’s just one cent per ounce.

To his credit, Kenney has earmarked where the soda tax revenue should go and has not tried to oversell its public-health benefits although studies have shown that consumption of sugary drinks contributes to obesity, diabetes and related ills.

That being said, is it possible we could design an even better version of this tax? Consider what’s happening in the United Kingdom. Beginning in 2018, the UK will charge the equivalent of  .75 cents per ounce for drinks that contain more than 3 teaspoons of sugar in an 8-ounce serving and a full cent per ounce for drinks with more than five teaspoons per serving.

The UK’s innovation is in the tiering, according to an analysis by the Tax Policy Center in Washington. Rather than hit all sugary drinks with the same tax–as Philadelphia is proposing–the UK has three levels. Drinks with little sugar aren’t taxed at all, drinks with moderate sugar face one tax rate and drinks with lots of sugar face a higher one.

The Tax Policy Center analysis concludes that the three-tier structure will encourage people and businesses to favor lower-sugar drinks over sweeter ones. “That’s important because sugar content differs significantly.  If you believe sugar is harmful, you should want people not only to cut back on sugary drinks, but to switch to less sugary options. And you’d want businesses to devote product development, marketing and pricing efforts to lower-sugar options.”

The analysis said linking the tax to sugar content encourages businesses to do that. Indeed, the UK is delaying the new tax law until 2018 to give beverage companies time to avoid or lower the tax by reformulating their products.

But the Tax Policy Center said the tax is far from perfect.  They asked: “Why do the tax rates differ by only a third when the difference in sugar content is often larger? Why not have even more tiers–or even directly tax sugar content?”

Those are good questions but they don’t diminish diminish the fact that the UK’s approach makes much more sense than taxing sugary drinks uniformly, as Berkeley does and Philadelphia is proposing to do.Those taxes do nothing to encourage consumers and businesses to favor lower-sugar drinks.

If we’re going to impose a sugary-drink  tax, let’s at least target sugar content rather than drink volume.