However, this figure may be more in the summer and winter months (ie you may have more than a couple of showers a day in the summer, and you will have your heating on more in the winter).
I live, on my own, in a tiny one-bedroom house which will have about the same running costs as a small flat. I pay everything by direct debit so that I pay the same every month (irrespective of whether it's winter or summer).
A quick glance at my bank statement shows that my combined gas & electricity bill is �32 per month. I'm also paying �21 per month for water. So my expenditure is rather lower than that suggested by STAH (and also less than the �62 per month I pay in Council Tax).
It is definitely worth having a water meter fitted as I live alone and only spend �8 a month on water - and about �40 on gas and electric (although I live in a two bedroom house rather than a flat).