|Data on the structure|
|Height of the barrier structure :||21.3 m|
|Data on the reservoir|
|Reservoir length||670 m|
|Reservoir width||390 m|
|Storage space||0.73 million m³|
The approximately 670 m long and 390 m wide lake is located in the south of the Council Area Edinburgh on the western flank of the Pentland Hills . The next town is Balerno, two kilometers to the northwest . To the southeast rises the 449 m high Hare Hill . The brook Bavelaw Burn , which rises a few kilometers south on the slopes of East Cairn Hill , feeds the Threipmuir Reservoir directly to the southwest . The dammed water from this lake flows over a weir into the Harlaw Reservoir. Leaving this via a weir on the northwest side, the Bavelaw Burn flows into the Water of Leith , which eventually drains into the Firth of Forth .
The Scottish engineer James Jardine is responsible for the planning of the reservoir . The construction, which served the water supply of Edinburgh, began together with the Threipmuir Reservoir in 1843 and completed in 1848. Although the state water supplier Scottish Water operates the dams today, the water is no longer fed into the drinking water supply. Together with the Threipmuir Reservoir, however, the Harlaw Reservoir still makes a significant contribution to flood prevention along the Water of Leith. In addition, the Harlaw Reservoir is regularly stocked with rainbow trout to provide a destination for local anglers.
On the north-east bank, a reinforced embankment, 157 m long and 21.3 m high, dammed the lake. The Harlaw Reservoir can hold 730 million liters of water. This means that its capacity is only around a third of that of the Threipmuir Reservoir.