Might I offer:
Iuvenes delinquunt quod bibunt in qua fluit plumbum aquam.
It's funky with its syntax, but it works. It translates to:
Youth are failing because they drink water in which flows lead.
Another suggestion is:
Iuvenes delinquunt quod bibunt aquam plumbeam.
The problem with this one is that aqua plumbea would mean "water made of lead," not really "water with lead in it." However, if you're deliberately trying to be enigmatic, it might work.
While I wrote iuvenes, you can easily use juvenes, though writing j or consonantal i isn't terribly fashionable anymore.
Let's also take a look at what you wrote:
Here, juvenis would indicate a single young person, so you'd want the plural, juvenes. Delinquitur is not only singular, it's passive, which would mean that one youth is being drunk.