Scottish Water's Alliance Partner Caledonia Water Alliance (CWA) finished the work six weeks ahead of schedule, with work originally set to last until mid-May.
Features included installing a total of 3.8km of new pipes to reduce the risk of bursts and interrupted supplies.
A CWA spokeswoman said: "We completed this project well in advance of the proposed date. This was down to having good communications with Midlothian Council's roads department and the skills of our sub-contractor R4 Utilities workforce in this type of work.
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"The inclement weather cost approximately two weeks of productivity so we would have completed even sooner had the weather remained dry."
A Scottish Water spokeswoman said: "Customers are at the heart of everything we do at and we understand roadworks can be frustrating for commuters.
"We want to thank drivers and commuters impacted by traffic measures used in this project for their patience while this essential upgrade to the water network took place."
(LM)
