Excellent siteJust had a look on the OS overlay on Bing Maps. There are three waterfalls marked within a km or so east of the centre of Alston on the river Nent.
Also have a look at this site - http://www.geograph.org.uk/ - You can search for all sorts of features (eg waterfalls) near anywhere.
Dave

Is that way good for bad knees as well I thought it was a bit rocky on the lower part of the fall fantastic view thoughThere's also Cow Green Reservoir a few miles to the South of Alston.
Take the minor road to the car park by the shore, then a walk of approx 1 mile of a farm track (There's a gate so you can't drive down) gets you to the foot of Cauldorn Snout. That is worth seeing.
Carry on that road and you'll come to High Force. You have to pay to park in the hotel car park then it's a short walk on a good track to a most impressive set of falls. Well worth the trip.