Is it forbidden or permissible to report a neighbor who tampers with the electricity meter and frequently uses the water pump shared between you, thereby exposing it to damage?

You should advise your neighbor with good counsel and remind him that the device is a trust that must be protected. If the advice is not effective, it is permissible to report him to the competent authorities, because this falls under the category of enjoining good and forbidding evil, and is not forbidden backbiting.