Trentabank Reservoir near Macclesfield in Cheshire was officially opened by Prince Henry, the Duke of Gloucester, in 1929. Luckily the event was captured on newsfilm.
Macclesfield Forest, where Trentabank Reservoir is found, is partly in the Peak District National Park in England. At the time the reservoir was opened, it had a capacity of 139 million gallons.
It cost £210,000 to construct. A great sum in 1921!
Reservoir at Macclesfield opened by Duke of Gloucester (1929) –
British Pathé (YouTube)