Gas for water heating

Hi Everyone,

I live in an apartment in Taipei with another person which likes very much to take a shower. That person is pretty consistent at 35 minutes each time, sometimes twice a day.

I am a bit worried about the gas bill, and when I saw the pink sheet sticked to the main door that we have to fill out, I saw that the landlord had put a little less than 13 000 in the column 度数 (level?). Another person had put something like 1 400 for his or her apartment, so by comparison, ours is much higher, and that confirms my initial preoccupation.

I am wondering how to interpret this number, and how does it translates into actual cost?

Thanks a lot.