The £30k investment at Tees Cottage Pumping Station, funded by Northumbrian Water, has seen the full floor inside the West Engine House replaced and a host of other refurbishment work taking place.
The recently completed works included; temporarily lifting out three tonnes of machinery and other equipment, stripping some areas back to the brick work, re-plastering, and building a new block and beam floor.
An archaeological survey of the four metre pit underneath the West Engine House also unearthed a large brass base of the site's original bearing case, which will go on display in the museum in future for visitors.
Peter Hall, Facilities Team Leader at Northumbrian Water, said: "The new flooring looks fantastic and a big thank you to the museum volunteers for their support, our partners and approved contractors for helping to deliver this essential work.
"We feel so proud of this historic landmark and of the partnership we have formed over the last 40 years with the volunteers, who do an incredible job helping us to preserve this spectacular place for generations to come."
Tees Cottage Pumping Station, built in 1849, once supplied drinking water to Darlington and the surrounding areas, until it was converted into a museum.
The historic site is still owned by Northumbrian Water and has two original pumping engines, with one being the largest preserved example in Europe and are superb examples of Victorian architecture.
Chairman David Smart, who has been volunteering at Tees Cottage Pumping Station for the last six years, said: "We are really delighted with the new replacement flooring and would like to thank Northumbrian Water for their continued support.
"The site has really transformed over the years and this is down to the amazing support of our partners, and the dedication of our wonderful museum volunteers."
For more information about Tees Cottage Pumping Station and to take a free virtual tour around the site, visit: www.teescottage.co.uk