Stonehouse Leat has nothing to do with Dartmoor, it ran entirely within the boundary of today's Plymouth: it is included here as part of the story of Plymouth's water supply.
In 1593, two years after Plymouth Leat started flowing, a similarly worded Bill was laid before Parliament to enable a leat to be built to supply the then-separate town of Stonehouse. It was considered by a committee of which Sir Francis Drake was a principal member - the same committee that a few days previously had rejected the Plymouth Leat Mills Removal Bill. The Stonehouse Leat Bill was modified to include a condition that no mills were to be built along it, with punitive penalties involved, thereby protecting Drake's own financial interests in the area - friends in high places! The Bill had a swift passage and became an Act for the "Bringing of Fresh Water to the town of Stonehouse in the County of Devon, 1593" (see 2 April 1593). Work began in the following June and it is believed that it took only a few months to complete the project.
The leat took water from Millbrook Lake and its tributary streams, about three miles from the town centre, in an area now known as Torr. 'Lake' is a local name for stream or brook. The leat wended its way to Mill Pool at Mill Bridge, Stonehouse, but its supply was never really adequate and in 1688 the town had to ask Plymouth for help. This was given until 1713 when Plymouth reversed their decision because of their own increasing demand for water. It is believed that the original sources may have dried up and that the leat was filled by water from Plymouth Leat by various clandestine methods. This might have been done at a point near today's Torr View Avenue where the leats crossed or near Houndiscombe Farm, Mutley, where Stonehouse Leat was crossed by a waste stream from Plymouth Leat. Stonehouse also received water from Dock (Devonport) a little before 1806, as the recently completed Dock Leat brought in abundant supplies of water. There were various improvements made but by 1893 the leat was falling into disuse as Stonehouse became supplied by Plymouth's Hartley Reservoir. The last few yards of the leat were finally lost during development in 1978.
For full details, see the David Hawkings book, pages 39-49.
One of the few remaining signs that Stonehouse Leat existed, in Cecil Street, a few yards from its junction with North Road West, Plymouth. It is illustrated by Hawkings (published 1987, page 47) with a pointed cap of cement but this has clearly been removed in the photograph above so that the stone has its original appearance. This photograph was taken in January 2013.
The David Hawkings book reports that only five of these stones remain out of a total of ten, see Appendix F, pages 74-78. They were of two types with different inscriptions:
(1) "Stonehouse Leat and Banks 1593"
(2) "1883 East Stonehouse Local Board Leat" (some, 1884).
Google Street Map of the location - the stone is a little below the lower 'Cecil Street', towards the lower end of the white garden wall, beside the blue door.
GPS location SX 47081 54995 ± 3 metres.
A second stone approximately 250 metres from the stone above, in North Road West, Plymouth. This stone has a different inscription to the first stone:
Google Street Map of the location - the stone is in the centre of the map, against a short white-painted garden wall.
Google Street View of the location - the stone is to the right side, against a white-painted wall on the pavement.
GPS location SX 46863 54908 ± 3 metres.
The stones are all believed to date from the early 1850s.
It is fortunate to find two surviving stones that show the two different patterns of inscription only about 250 metres apart.
The octagonal water tower in the grounds of the Royal Naval Hospital, Stonehouse, that was fed from Stonehouse Leat by a chain pump. The hospital was built in 1758, the tower was built later after 1778 when the hospital asked for a water supply from the leat that ran through its grounds.
Google Street Map view of the Octagonal Tower - the end of North Road West can be seen at top centre of the image.
Google Street View of the water tower - you can drag your way to the left in this image to look along North Road West, then click on the pavement just past the lamp post on the right and you can then see the second stone above.
Just for fun ...........................
..... this is the first "antiquity" that I have photographed sitting, parked in the car!
Reference: Water from the Moor - An illustrated history of the Plymouth, Stonehouse and Devonport Leats, by David J. Hawkings (1987), Devon Books, Exeter.