im paying 40 pound a month with out a meter,but if had a meter couild be as little as 15 a month,.but im filling up every day 250lts,so at the moment im happy without meter,if i had a meter i think the 15 a month would sky rocket,will be interested to find out though.dont know about being compulsery,but if you get one installed and sell your house it has to stay buyer carnt switch back