The equivalent of 1½ times the capacity of the original Cotter Dam has been added to the ACT's water reserves in the past 10 days, ACTEW Water figures show.
As a result, Canberra has more water in its combined storages going into autumn and winter than ever before.
Following 42.8 millimetres of rain at the weekend, there is almost as much water in the Corin, Bendora, Cotter and Googong dams now as on January 1.
Water levels usually dip noticeably over summer as consumption increases and inflows are reduced.
The four dams are at 73.6 per cent of their combined 278 gigalitres capacity; compared with 75.8 per cent at the beginning of the year.
This is a gain of 2.3 per cent, or 6.3 gigalitres, on the 71.3 per cent recorded at the end of last month.
Before a major upgrade, completed between 2009 and last year at an estimated cost of $409 million, Cotter Dam could only hold 4 gigalitres of water.
It underwent a 72 gigalitres capacity boost as part of a multipronged strategy to dramatically increase Canberra's water security after the devastating 2006 to 2010 drought.
The Centre for International Economics, Canberra and Sydney has estimated the annual cost of the stage three restrictions in place in Canberra from late 2006 to 2010 at $75 million a year, or more than a $250 million over that time.
About $4 million a year of this was borne by industry. The bulk of the impact was felt by householders and residents through loss of amenity, the destruction of gardens, lost time to hand watering and the like.
The good news, according to ACTEW Water's group manager for customer solutions, Chris Webb, is that water restrictions are effectively a thing of the past for Canberrans.
He said the region would have to experience a drought of unprecedented duration and severity for it to be necessary to introduce water restrictions again. Permanent water conservation measures are now in place, however.
''We have secured the provision of water [for the ACT] for a generation or more to come,'' Mr Webb said. ''We are in a completely different situation to where we were at the start of the last decade.''
He is confident three of the four dams will receive a top up over the rest of autumn, winter and into spring. Googong's water level is unlikely to rise by much, given it now stands at 99.6 per cent of capacity. Bendora is at 91.9 per cent and Corin is at 56 per cent.
The new Cotter Dam, which only started taking water on February 23 last year, had reached 30 per cent of capacity by its official opening in October last year and was up to 41.6 per cent on January 1.
''Increases to dam levels depend on a number of factors beyond rainfall,'' Mr Webb said. ''We also take into account community consumption, the condition of the catchments, where the rain falls and evaporation,'' he said. ''Now that our catchments are in better condition and consumption is decreasing, any further rainfall will have a greater impact on overall levels.''
He said under ''normal conditions'' the new Cotter Dam would take about five years to fill.