With one day to go before the May 21 special election, only around 22 percent of Multnomah County voters have returned their ballots.

That’s well above the 11 percent that had voted at this point in the May 19, 2009, Special Election. Ultimately, only about 15 percent of county voters took part in that election.

But the response is only slightly better than the 20 percent that had voted at this point in the May 17, 2011, special election. Ultimately, a little more than 36 percent of county voters retuned ballots in that election.

The participating rate in Tuesday’s special election is surprisingly low, considering that neither of the previous two May elections had any controversial measures on the ballot. In contrast, an emotion and expensive battle is being waged over the measure to fluoridate Portland’s water.

Both sides claim to be most concerned about the health of the city’s children, and are accusing the other side of misrepresenting the facts. They are both running TV and radio spots, and paying for direct mail pieces.

The two campaigns have so far raised more than $1.1 million in cash and in-kind contributions. The committee in support of Ballot Measure 26-151 reports more than $845,000 in donations. The committee opposing fluoridation has raised more than $269,000.

Two other measures on Portland ballots are also drawing significant support. The committee in favor of Measure 26-151, which extends the Portland Children’s Levy, reports raising more than $381,000. The committee in favor of Measure 26-152, to help maintain Metro’s open spaces, has raised more than $268,000.

The rate of returning ballots should increase steadily during the next week. Both sides in the fluoridation fight also have volunteers going door to door to identify supporters and make sure they vote.

Ballot should be physically returned to the Multnomah County Election Office or officially designated drop sites to guarantee they are counted. Addresses are available at web.multco.us/elections.