ESPN is reporting that several NFL players have tested positive for banned substances, at least half of them being found to use a water pill that helps the user to lose weight.
This may seem confusing to some, since a water pill is not in and of itself a steroid, nor will tanking up on water pills make you a better football player. However, the diuretic Bumetanide can also be used to mask steroid use, so testing positive for that sends up a warning signal.
To explain, it's like banning Pacman Jones from using alcohol, then testing him every Friday night for an overuse of breath mints to see if it seems fishy.