Victoria's near-record dry winter has pushed Melbourne's water storages close to the level where the state will start to prepare for drought, which could involve cranking up the multibillion-dollar desalination plant to its full capacity for the first time.

A new threshold set by the Andrews government requires the state's water corporations to begin to prepare for drought should Melbourne's water storages drop below 60 per cent by November 30.

The previous threshold was 54.1 per cent.

Melbourne's dams are 62 per cent full and dropping towards the new mark following the state's driest June since records began in 1900. Many parts of the state received less than 20 per cent of the average monthly rainfall.