My father-in-law has always been a faithful user of Rain-X which is a coating you apply to your windshield and it makes visibility much better while driving in the rain. The problem with Rain-X is that it must be applied exactly as the directions state. Another problem I've found that it works great the first time you apply it, but subsequent applications kind of muck things up. The only way to make it right is to replace the windshield or clean it off if you can and replace with wipers in the process.
My wife has been driving her father's car and the Rain-X coating was so bad that she insisted I study sites on how to remove it. Rain-X is considered the bane of window repair shops. Many don't even want to work on windshields that have ever been treated. The suggestion was to use Soft Scrub or Bon Ami or similar products that do not scratch to remove the coating. I tried Bon Ami and the stuff just beaded up on the windshield. It didn't remove anything even with vigorous scrubbing. Next I moved onto glass stove top cleaner and this worked like a charm. It actually removed the stuff.