The best case scenario is a foreign irritant or something got into your rabbit’s eye (like a piece of hay, stubborn eyelash or fur strand), causing it to water and it will resolve on its own in… an hour tops, as a guestimate. Resolving means no more watery eye, as well as all health-related behaviors being normal (energy, poop, pee, appetite, body language).
If it does not resolve on its own and/or health-related behaviors begin to decline, there may be an injury. When it comes to the eyes, unfortunately a vet assessment is needed, as they have the proper equipment and drugs to assess the nature of an injury and what is needed for tx.
For now, depending on the intensity of the watering, you can help your rabbit out a bit by dabbing the area gently with a soft towel occasionally so the skin and fur does not get too irritated. Also make sure your rabbit has consistent access to hay and water. A couple pellets as treats wouldn’t hurt either.
If there is any chance this is an injury caused by the other rabbit (because they are not fully bonded/are young rabbits, for example), I would separate them for now. If they are truly bonded rabbits (adults), you can keep them together, but monitor if the other rabbit may be irritating the eye unnecessarily via grooming or other means.
If there is any blood or colored discharge, that becomes pressing to go to a vet as soon as you can to get a proper dx and the necessary treatment.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.