A toilet bowl cover apparatus, for use on a toilet having a toilet bowl and a seat, includes an arcuate frame member configured to surround or fit on top of the toilet bowl below the seat. The cover apparatus also includes a flexible plastic sheet member having a shape configured to fit on the frame member, the sheet member having an upper side and a lower side with a sticky adhesive material thereon. The cover apparatus is configured to adhesively attach to an upper surface of the toilet bowl, in order to substantially seal the bowl and minimize water evaporation from the bowl during periods of non-use.