Dazzdax,
I have ruined records with tap water. Unless you run a chemical and particulates analysis on your water, get results many standard deviations purer than normal, and have confidence that those results will remain consistent going forward, you're merely guessing about what's going on your vinyl.
That might be an acceptable risk with a grungy $.25 thrift store find, but reissues and increasingly rare originals at $30+ a copy deserve more careful treatment.
And no sponge, cloth or brush can remove scummy liquid from inside the grooves. The grooves are too small. Only vacuum at fairly high velocities can do this.
A phono cartridge is a motion detection and amplification device. The better ones reliably generate electrical signals from even sub-micron deflections of the stylus. Put another way, top quality systems amplify stylus deflections by factors of 8,000 or even more. Therefore, any impurity above molecular sizes will be detected and amplified by a good system. Even those who don't have such systems today would be prudent to care for their records on the assumption that they might, someday.
Doug