You scour, you scrub, you rinse and you repeat. And yet those pink stains keep popping up in your sink. What are they and why won't they go away? They could be caused by a couple of things, so you'll need to do a little troubleshooting before determining your issue.
One of the culprits could be too much iron in your water, which is more often a problem for people in rural areas who use well water as their water source. These types of stains start out more red and fade to a pinkish color. Fortunately, the problem is easily remedied by having a water filtration system installed. Just be sure to determine where the iron is coming from and its type so you get the right filter.
Another cause of pink stains is a type of airborne bacteria called Serratia marcesens, which occurs naturally in food, soil and animals. It thrives on moisture and feeds on itself, so it doesn't need a particularly accommodating host to survive. It's commonly found during construction or remodeling projects, which tend to stir up dust containing this bacteria, but it can also enter through an open window in the summer. It's generally found to be harmless for healthy people, though it has been linked to urinary tract infections and pneumonia. Chlorine bleach is the easiest way to keep the pink stains at bay. Be sure to keep sinks wiped down so that water doesn't pool and beckon the bacteria.