Roundhill Reservoir is situated near Leighton Reservoir in North Yorkshire, England. It was constructed by Harrogate Corporation early in the 20th century. Water from the reservoir is fed into Yorkshire Water's grid. Roundhill reservoir is overlooked by a strange stone tower. This is Carlesmoor sighting tower used to triangulate the end points of a water tunnel from the reservoir to Harrogate. It is one of several Colsterdale towers. Although not in Nidderdale, the reservoir is within the Nidderdale Area of Outstanding Natural Beauty.