As long as you are not experiencing an actual flow of blood (comparable to a period), you may take precautions against becoming niddah from any staining by wearing colored underwear (or disposable pantyliners) and waiting at least a few seconds (ideally 15 seconds) after urinating before wiping in order to disregard stains on toilet paper.

There is no need to feel guilty about disregarding such staining. The laws of stains (ketamim) are a rabbinic stringency added by our Sages onto Torah Law. However, in order not to overburden women and cause them to become niddah frequently from staining, the Sages built certain leniencies into these laws. Stains found on colored surfaces, or on disposable surfaces such as pantyliners and toilet paper, were never intended to render a woman niddah. Therefore, you certainly should take advantage of these leniencies to prevent becoming niddah (unnecessarily) from staining.

Please feel free to get back to us with any further questions.

B’hatzlacha!

This response has been updated to reflect the rulings of our current Rabbinic Supervisor, Rav Kenneth Auman, regarding waiting before wiping.