Thanks Jamie, I've just checked my last Severn Trent Bill (April 2010 - Oct 2010)
Water supply 74m3 @ 136.51 pence per m3 - £101.01
water standing charge - £13.55
Used Water 74m3 @ 83.68pence per m3 - £61.92
Used water standing charge - £6.37
Measured drainage - Band 03 - £43.33
I was £29.71 in credit so they increased my direct debit from £37 pm to £45 pm
I don't actually know what any of the above means but I've just read my meter and I've used 33m3 water since the last bill almost 6 months ago.
In hindsight, the last bills would have been based on usage when my ex-wife was still living in my house, so usage will have gone down now.