What is the ruling on us using water from behind the meter?

Manipulating the water meter and using water without payment is forbidden, because it is an encroachment upon the property of others without a just cause, whether the "other" is an individual or a public entity. Whoever commits such an act must repent and clear their conscience by returning the money to its owners if they are identifiable. If the money belongs to the public, it is obligatory to dispose of it by spending it on charitable causes if it is impossible to return it to the competent authority.