Citric acid is a weak acid found in fruits such as lemons and oranges. You can also find it in commercial fruit drinks and certain household cleaning supplies. Like other acids, citric acid can help you remove stains and rust deposits from toilet bowls without causing any damage to the porcelain surface.
Why It Works
Acids cause mineral deposits such as rust to oxidise, thereby weakening them and making it possible to simply wash them away. Other weak acids, such as acetic acid (found in vinegar) and phosphoric acid (found in soft drinks) can have similar effects, but unlike these harsher products, citric acid contains just enough acidic concentration to get the job done without etching or damaging household surfaces in any way.
Sources of Citric Acid
You can obtain natural citric acid by squeezing or juicing lemons. Certain fruit drinks contain citric acid in both powdered and liquid form. Just look for "citric acid" in the list of ingredients. Natural and green all-purpose cleaners sometimes advertise the presence of citric acid on the label. Colas such as RC, Pepsi and Coke contain small amounts of citric acid but also contain larger amounts of phosphoric acid (a much stronger acid), so use them sparingly.
The Cleaning Procedure
You can use citric acid in either its liquid or powdered forms. Just pour or sprinkle the citric acid product along the inside of the bowl and let it sit for at least two hours. When you return, flush the toilet and all mineral deposits should vanish. You can then scrub the bowl with your favourite toilet-bowl cleaner for a more thorough shine. To clean the outside of your toilet, moisten a soft cloth with lemon juice and scrub away.
Unlike many commercial toilet-bowl cleaners, citric acid contains no fumes or harsh chemical compounds. You need not worry about breathing in volatile compounds or using products that harm the environment. As an added bonus, citric acid (due to its oxidising properties) removes rust with greater ease than some commercial products, so you will not need to spend as much time cleaning. Since citric acid functions as a natural deodoriser, making your bathroom smell fragrant as well.