None wrote:

I changed my dishwasher the other day to be horrified at the amount of
mud underneath the old unit. I then checked under the dishwasher...
same. To see the extent of the problem I drained the attic tank, and
there was a thick brown sludgy mess at the bottom also. I wonder is it
due to a mains leak somewhere? Any help/advice on this would be great.
I'm on a mains water supply with strict regs... so I don't think this
should be happening?!

Sorry, meant to say I changed my washing machine...