Grout seals the space between tiles, but the cement or epoxy tends to darken with everyday use. Soap and hard water in a shower aid the growth of mold and mildew, causing discoloration. Heavy traffic on floors leads to dirt and buildup between tiles. Clean discolored grout with a solution of oxygen bleach and water. The oxygen bubbles penetrate the porous or sealed grout to clean, disinfect and brighten. Use oxygen bleach in place of chlorine bleach for a fume-free substitute.
Fill a spray bottle with 2 to 4 tsp. of oxygen bleach. Allow the mixture to stand for five minutes. Replace the lid, and shake it up until the powder fully dissolves.
Spray the grout and tile with the oxygen bleach. Completely soak the grout with the solution, and allow it to sit for 30 minutes.
Put on the gloves, and scrub the grout with a brush. Use more cleaning solution if necessary.
Empty the spray bottle, and rinse it well with warm water. Refill it with clean water, and spray the tiles and grout to rinse away the cleaner. Spray and wipe with a cloth until all of the residue is gone.
Dry the tiles and grout with a soft cloth or towel. White grout won't appear bright white until it's fully dry.