This is the pond in Watford High Street as is was in the 1900s. It has existed here since at least 1849 and is probably much older, being used originally as a "drive through" water trough designed to cool and wet (swell) wooden cart wheels, and to refresh the horses on their journey into and out of London. It is the only one remaining out of four in the town (the others being at Clarendon Corner, Rickmansworth Road and Cashio Hamlet). Nowadays it looks completely different.
It is located at position 14 in green on the map.