The reservoirs at Bohernabreena were constructed between 1883 and 1887 for the dual purpose of supplying Rathmines with drinking water and of ensuring a constant supply of water to the many mills along the River Dodder. There were, at the time, forty-five mills served by the Dodder, of which fifteen were flour mills. The rest consisted of paper, paint, cardboard, cotton, saw, glue and dye mills, as well as distilleries, breweries, malt houses, foundries, tanneries and a bacon curing factory.
The waterworks consisted of two impounding reservoirs, the upper or clear water reservoir and the lower or mill owners’ compensatory reservoir. The gathering ground consisted partly of bog land which comprised the mountainous area around Castlekelly and stony land free from peat which lay on both sides of the glen. It was from the latter area that clear water was collected into the upper reservoir for drinking purposes. The peaty water off the bogs bypassed the upper reservoir in an artificially constructed channel. At the upper end of the mill owners’ reservoir there was a guage which allowed 1500 cubic feet of water per minute to pass into a pipeline through which it was conveyed into the natural river channel below the dam. The surplus water was diverted into the lower lake where it could be held until it was needed.
Today, Bohernabreena Waterworks is still vital to Dublin’s water supply. Water is pumped from here to Ballyboden Treatment Works and it supplies millions of litres to the city every day. The Waterworks are also a popular spot for walkers and are part of the Dublin Mountains Way. The shores of the reservoirs are clothed in a mixture of trees and shrubs and bird species present in the area include gulls, kingfisher, dipper, grey wagtail, heron and moorhen.
For further information see http://source.southdublinlibraries.ie and http://www.dublinmountains.ie
South Dublin Libraries Local Studies 
Nice write up, was up here today and was curious as to what the main function of the dams were. Its such a beautiful area, and dangerous one too in light of the accident during the week.
Loved reading this. My grandfather was the gatekeeper there for many years, and before that, he worked for the Forestry Commision, planting the trees and shrubs there.
Nice information but can I just give you one correction. The start/finish of the Dublin Mountains Way is the Sean Walsh Park, Tallaght, not the Waterworks as you say in the above post. Thank you.
It is only while working from home I discovered some comments that had not been responded to. I have corrected the blog post. Many thanks for pointing it out to us. better late than never.