If you are attempting to tackle your oven mix one cup of baking soda with one quarter cup of washing detergent , add water to make a paste. Smear the paste on oven surface and leave overnight. Just wipe off in the morning!
Showers are always a problem at my house. A squeegee and vinegar is your answer! It only takes a few moments to squeegee a ceramic tile shower, but it will keep those hard water spots from build-up. You can wipe the shower once a week with full strength vinegar . If you need to soak the shower head or metal parts soak in 1 part vinegar to 8 parts water and simmer for 15 minutes.
Windows are most important as the spring sun begins to shine daily. One cup of white vinegar to one cup of water. pour the mixture in a spray bottle and wipe with old fashion paper towel or news print works just as good. You will have minimal streaking ! (consumer reports on health vol.25 number 4.)