Hard Water Stain Remover
Mix one tablespoon citric acid with one cup of water and use it to gently remove hard water deposits from shower glass, sinks, etc. with no scrubbing needed!
Multi-Purpose Bathroom Cleaner
Diluted vinegar (a 1:1 ratio of vinegar to water) or diluted liquid castile soap (a 1:16 ratio of liquid castile soap to water) are effective solutions for general bathroom cleaning, but sometimes a stronger solution is necessary.
Mix the warm water and baking soda first, then when the baking soda is completely dissolved, slowly add in the vinegar (to avoid the fizzing reaction that vinegar and baking soda usually create). Pour into a spray bottle for use.
Clean a toilet by pouring a half cup of baking soda into the bowl, followed by a cup of vinegar, and allow the two ingredients to react. After the reaction dies down (or just go do something else for 5-10 minutes), scrub with a toilet brush and flush the toilet.
Shower Head Cleaner
Submerge the shower head (facing down) in the above solution (after it is mixed and the fizzing dies down). Either the shower head can be removed and placed in a bowl with the solution, or a small bag (containing the solution) can be tied around the submerged shower head. In either case, wait about an hour, then remove the shower head from the solution and rinse it thoroughly before its next use.
Mold & Mildew Cleaner
Citrus enzyme cleaner is one solution to help cut mold and mildew, and vinegar (especially combined with lemon juice) is another. Either should be sprayed on the moldy/mildewy surface and left to set for several minutes before the surface is wiped clean. Regular applications will help to prevent new growth of mold and mildew.