"He does not need more water."
Translation:Él no necesita más agua.
Verbs don't change form according to the gender of the subject, they change conjugation depending on the subject only:
necesitar - to need
yo necesito - I need
él necesita - he needs (also ella/usted)
tú necesitas - you need
ellos/ellas/ustedes necesitan - they/you (plural) need
nosotros necesitamos - we need
Are they speaking about a plant? Do you have to use personal pronouns for al living things? Are mushrooms gender specific? Or are they speaking about a goldfish in a bowl? Do you have to use personal pronouns for animals? I always say 'it'? Or are they talking about someone who can't talk and is this said by the person who understand sign language to the person who don't?