I'm not sure about NTL (or Telewest etc) as these are regional 'cabled' networks.
On installation, the SKY engineer 'tunes' in your SKY digibox to your local 'default' ITV regional channel based on your postcode. However, the satellite is transmitting all ITV regions throughout the UK.
BBC regions however, for some reason, appear in the usual channel line-up (somewhere in the 900's).
BTW
Water World used to be repeated a few weeks later on a Friday afternoon in the Carlton London and Carlton West regions. Whether this is the case for this series remains to be seen.
Water World is also re-broadcast the following year on the Discovery Channel.
The series will not be made avaialable on VHS or DVD as Series 1 sold too few copies to make it commercially viable.
The series is aimed not only at Inland Waterway enthusiasts, but mainly to a general viewing audience. In the Carlton Central region, over 1,000,000 viewers watch it each week and Series 1 achieved 37% of the viewing audience against competitors especially 'EastEnders'. In itself, no mean achievement.
What makes it popular amongst a general viewing audience is not that it's a series strictly about canals, but about interesting people who live and enjoy an alternative, enviable and/or unusual lifestyle.
It's not broadcast nationally because the Central Region has a higher proportion of canals than elsewhere in the UK.
How do I know all this technobabble?!
Because I was research associate on Series 1 and caught the documentary making 'bug' and went on to graduate in the 'Moving Image (Factual).