iPhone 6s main camera not working

It can be surely related to unusual circumstances like rain when nothing else special has happened to the phone previously, water manages to get more or less everywhere. Since it’s clean distilled water maybe it didn’t do any major damage to the logic board..try removing the screen and camera to check if there’s any humidity trapped there in the connector. Try letting it dry at open air, possibly a dry ventilated place for a day, you can also blow some moderately warm air with a hair dryer. Then try again if camera works, if not buy a replacement part..if yet it stays black it’s likely some component got shorted and needs replaced, but that would require microsoldering skills and tools.