if anything you may have some heavy metal issues with iron possibly but the check valves from marine depot are relatively cheap, also you may want to consider just using an antisiphon hole in your return, (in-tank side of course) maybe at the top of the return in the loc line, all you need a very small pinprick type hole (mine is around 1/16) of an inch which allows for a minimal amount of water to be sucked back through the pump before the siphon is broken, this method very rarely fails as long as the water flow isn't interrupted for very long (more than a few days) at one time, and is pretty much free unless you don't have access to a drill and small bit.