"x x x.
“Legal standing” or locus standi has been defined as a personal and substantial interest in the case such that the party has sustained or will sustain direct injury as a result of the governmental act that is being challenged, alleging more than a generalized grievance. The gist of the question of standing is whether a party alleges “such personal stake in the outcome of the controversy as to assure that concrete adverseness which sharpens the presentation of issues upon which the court depends for illumination of difficult constitutional questions.”24 This Court, however, has adopted a liberal attitude on the locus standi of a petitioner where the petitioner is able to craft an issue of transcendental significance to the people, as when the issues raised are of paramount importance to the public.25 Thus, when the proceeding involves the assertion of a public right, the mere fact that the petitioner is a citizen satisfies the requirement of personal interest.26
There can be no doubt that the matter of ensuring adequate water supply for domestic use is one of paramount importance to the public. That the continued availability of potable water in Metro Manila might be compromised if PSALM proceeds with the privatization of the hydroelectric power plant in the Angat Dam Complex confers upon petitioners such personal stake in the resolution of legal issues in a petition to stop its implementation.
Moreover, we have held that if the petition is anchored on the people’s right to information on matters of public concern, any citizen can be the real party in interest. The requirement of personal interest is satisfied by the mere fact that the petitioner is a citizen, and therefore, part of the general public which possesses the right. There is no need to show any special interest in the result. It is sufficient that petitioners are citizens and, as such, are interested in the faithful execution of the laws.27
x x x."