Earlier quoted context omitted.
The judge can only rule on the arguments and evidence presented in their court.
Yes, of course, but he interprets the arguments and evidence presented to them. Here he chooses to interpret what they say as demanding the recognition of a new constitutional right to safe water and to correct information. It is not at all clear that that's a good choice. He could equally well interpret the situation by analogy: the government deliberately tricked people into drinking unsafe water, and people were,…
> Every person who, under color of any statute, ordinance, regulation, custom, or usage, of any State or Territory or the District of Columbia, subjects, or causes to be subjected, any citizen of the United States or other person within the jurisdiction thereof to the deprivation of any rights, privileges, or immunities secured by the Constitution and laws, shall be liable to the party injured in an action at law [...]
and what they said they had been deprived of is their substantive due process rights.
The plaintiffs brought a Constitutional argument. The court ruled on the Constitutional argument.