Have you asked the three other units if they have hot water and, if not, how have they dealt with it? I would start off by writing a letter to the landlord, not the super, and have all the tenants sign the letter if they feel the same as you do. Then post it. Don't give it to the super. I'm not sure if this will do any good because at times landlords like to turn a deaf ear on what they hear but perhaps the landlord isn't aware of the situation.