Water at the base of a toilet usually means the wax ring has failed. The wax ring is the thick seal between the toilet horn and the floor flange that keeps water and sewer gas from escaping. Replacing it requires removing the toilet, scraping off the old wax, setting a new ring, and resetting the toilet. Moderate effort -- toilets are heavy (50-100 lbs) and you only get one shot at placing it on the new wax. But the parts cost under $25 and the repair prevents subfloor rot, mold, and sewer gas in your home.