I think the reason for that is there's no water equivalent of The National Grid.
Water companies themselves have to maintain the pipes and distribution network etc. Unless the government forms a new company to do that, which the water companies pay a fee per m3 distributed to, then there's no way to fairly switch supplier without there being major issues over costs.

this is dated August 2006, nearly 6 years ago ...
http://news.bbc.co.uk/1/hi/uk/5255218.stm

reasons given for not investing in a national water grid from north to south, west to east are given as environmental
but a high speed rail link from London northwards (right through the middle of England) up to Scotland costing billions is going ahead regardless of any environmental concerns

yet water is a natural resource needed by everyone, railways are not

but we do have a national canal network which can not only transport goods but funny enough water as well ...
http://en.wikipedia.org/wiki/History_of ... nal_system

It wouldn't work out that much more expensive for me to buy all my water from Tesco in plastic bottles.

Not sure they can help me with the sh!t though...

There you go again. You have to stop this sensible approach to things. It won't do, do you hear me?

Canals are very, very poorly utilised these days. Every so often, a BBC4 documentary about them pops up.I urge you watch it to see how idiotic things got.

It’s interesting to note how much water is “lost” when you empty a lock. Thousands of gallons. It goes somewhere, and it makes supreme sense for it to end up in a water processing plant rather than just sloshing into a river somewhere. As well as canals, there are areas on the navigation system where water is stored locally to replenish this lost water. The Victorians had it all worked out.

Even though there is a certain amount of outflow, canals were designed to minimise water loss and current. I have no doubt that the majority of boating traffic would have increased difficulty navigating up and down stream, narrowboats just weren't designed for it. Even if there is no traffic having a current is going to cause other problems with erosion and sedimentation.

They manage alright on most rivers they're allowed on.

And now, let's waste even more money....

http://www.telegraph.co.uk/earth/earthn ... rises.html

"According to official figures, the companies are losing 3.4billion litres of water a year to leaks, equivalent to 25 per cent of all water used. Thames Water admitted that its last hosepipe ban, imposed in 2006, resulted in just a 5 per cent drop in water use."