Need advice; Housemate has a Spa but all bills are split evenly.

I'm living with 3 people including myself, one housemate I live with has a Spa that he and only he alone uses. Our electricity bills are sky high high and I'm pretty sure beyond reasonable doubt that my roomies 4 man, 10 yr + old spa, is the reason for this. I've read online that older spa's can cost around $3 per day to run and like most older models, his spa in on 24/7. So thats a potential $1000 p/y to run this Spa, however we split all bills evenly.

I feel like its only right that the Spa owner should put more into the electricity bill as he's probably the one pushing up the bill so high but he doesnt agree. Shouldnt he have to be financially responsible for? If I bought a dog I wouldn't expect my roommates to pay to help me maintain it.

He's out a lot and says that since I and the other house mate are home more often, which is true, it shouldnt be an issue.

Has anyone been in a similar situation?

Just some details about our situation; we live in South Australia, which has the highest Electricity prices in the world. His mum is the landlord and basically told me that since I knew the spa was there when I moved in tough luck, however I didnt know what the running costs of a Spa were at that time.