I have found (in our home bathrooms -- one tiled, the other fiberglass) that a mixture of 1 cup vinegar (heated in microwave to very hot) and 1 cup of the old blue Dawn dishwashing soap in a squirt bottle works wonderfully. You do need to have good ventilation or leave the room a couple times because it is very strong smelling when spraying. All you do is spray it on, leave it for 30 minutes (or more) then rinse it off. I usually run a scrub brush (on a broom handle) over it when I first spray it on in order to make sure I have coated the entire surface but no elbow grease is necessary. The soap keeps the vinegar in contact with what you want cleaned and it seems to stay "moist". It doesn't foam up when you rinse it off and once dried the surfaces shine like new. It even makes my brass faucet and handle collar shine. All waterspots gone. I dry my tile walls after every shower, but still like the excellent shine of the tile once it and the jacuzzi tub it surrounds have been cleaned with this mixture (found the recipe online at Pinterest). The fiberglass tub/shower is smaller and takes less so I do 1/2 cup of each. Any that is left I spray into the toilet and let sit. Really works well on hard water ring, no more scrubbing with pumice stone! TMI, I know...we are on a well and our water is pretty hard.