What causes pus in urine? I've been noticing that when i urinate in a bowl...that's what my doctor told me to do to catch my stones last year and now, it's kinda a habit, i'm noticing that there are some string like things in my urine. My urine is seldom just my urine, but usually urine with these things in them which i'm assuming is pus. I would really appreciate any ideas about what this is exactly and what causes it?