After lengthy repairs to the National Gallery of Victoria's water wall, the drought broke on Wednesday when the steady stream sprang to life - anxiously monitored by gallery director Tony Ellwood.

A cracked glass pane forced the shutdown of the Melbourne landmark in early December. Children expecting their first watery baptism in art have been met with signs and maintenance works during the peak holiday season.

''I pushed for a new look and feel and campaign for summer, and here we've had this unwelcoming entrance which has really upset me,'' said Mr Ellwood, who took the helm of the gallery six months ago.

The pane has been replaced, but the silicone sealing the glass failed twice, with leaks forcing the gallery to stem the flow until now.

Philip Goad, professor of architecture at the University of Melbourne, has criticised the time taken to restart the popular attraction. ''The water wall was redone in the refurbishment back in 2002-03 so it shouldn't be failing. Sometimes things like this are technically complex but it shouldn't be that difficult to fix.''

Mr Ellwood defended the time spent on repairs, saying he wanted to guarantee the leaks were fixed.

The crack was discovered on a day of extreme heat, and could have been caused by ''thermal stress'', he said. He immediately commissioned an engineers' report, which he said was ''inconclusive'' about the cause of the crack. ''There's also the likelihood that the pane of glass may have had an existing fault.''

He didn't rule out that a mural painted on the water wall could have damaged the pane through the black paint absorbing heat. ''It's possible, we don't know.''

The engineers' report by Arup concluded that several issues combined to result in the crack. ''Namely, a black motif painted on the back of the glass causing the glass to heat up, the water had been turned off to facilitate maintenance work on the external ceiling above the water wall and a very warm day. The combination of issues was unusual and unfortunate in that it caused the glass to crack due to thermal stress,'' the report said. It found no structural issues of concern.

The gallery removed the mural, created by Indonesian artist Eko Nugroho ''primarily for safety''. (Each water wall pane measures 6 metres by 3.3 metres and weighs about 1.2 tonnes.)

Mr Ellwood said he hadn't anticipated problems with murals on the water wall because there had been precedents that didn't cause damage. He does recall that merely weeks after US artist Keith Haring painted on the water wall in 1984, vandals threw a hammer shattering the art and glass.

Before becoming director last year, after heading up Brisbane's Gallery of Modern Art, Mr Ellwood spent seven years as deputy director of the NGV when it underwent a refurbishment between 2001-04. The team of Mario Bellini and Metier3 controversially altered the Roy Grounds-designed 1968 St Kilda Road building, including the water wall.