REFURBISHING of the remaining Plumb's Chambers building was momentarily halted when a historic underground water tank was discovered.

The dome-shaped in-ground brick water tank or well was uncovered by earthworks on April 2 on the site at 84 Fitzroy St.

Its discovery brought a halt to restorations early this month but work has now resumed after the Department of Environment and Heritage Protection gave the all-clear.

EHP officers have visited the site and discussed the future management of the tank with McConaghy Group and consultants, who are preserving the building as part of the Rose City Shoppingworld expansion.

While the discovery - under a concrete floor of a former toilet block - has resulted in some minor delays, no changes will be made to the planned completion of the restoration in July.

Local heritage advocate Donna Fraser said the uncovering of the well was a substantial discovery and evidence of the site's significant history.

"The tank is described in the site's heritage citation and to now find it intact is very exciting," she said.

The Chambers' heritage listing states that a large underground water tank and pump existed at the site in 1882, then owned by Warwick chemist Charles Clarke.

"Clarke had put in the tank to have purer water for manufacturing of his pharmaceuticals because the river water was not clean enough," Mrs Fraser said.

"He was also a seed merchant and introduced many of the crops the Darling Downs is now renowned for."

The McConaghy Group advised they would carefully record and photograph the water tank.

The tank has been filled with stabilising sand and a new concrete slab is to be laid over the top of the tank, an approach supported by EHP.

Mrs Fraser said she would like to see the site preserved and have a permanent record of the tank's existence at the site.

"I would like to see it further enshrined as part of the interpretation of the heritage site, recording an important part of our agricultural history," Mrs Fraser said.

"Warwick has a rich built history as one of the country's first pastoral districts," she said.

"We have lost many of our heritage buildings to developments over the years, and I feel we should be concentrating on the tourism value of what remains of them."

It is expected the recording of the feature and careful backfilling will begin this week.

No. 84 Fitzroy St is being restored as part of extensions to the nearby Rose City Shoppingworld to be undertaken by McConaghy Group. No. 82 was demolished last year.