But in reality, laws are never perfect and all-encompassing. There is nothing wrong with Congress passing a law that says "water must be clean enough to drink", and then leaving it to a pool of experts to define "clean enough to drink" as "free from chemical X, Y, Z..." and to intervene when new chemicals show up.
Expecting the already-clogged lawmaking process to be ready to amend a law every time a new compound ends up in water, is extremely unrealistic.
As French, our dual-branch judicial system for a long time seemed very weird to me — I didn’t really see the point of it. I must thank the US to provide a clear example why it is in fact so useful.
In France, the law would be typically written as "The water must be safe to drink. The list of banned chemicals and safety thresholds is to be set by the Supreme Court of the Administrative Branch" (Conseil d’Etat). That way you still do have a judicial oversight of agencies, but with a judicial branch which has more adapted procedures to those issues (for example you don’t have to wait for a case to go all the way up to the Supreme Court to adjudicate — it is literally part of the job of the Supreme Court of the Administrative Branch to be proactive in those matters).
Expecting the already-clogged lawmaking process to be ready to amend a law every time a new compound ends up in water, is extremely unrealistic.