Melburnians are being put on notice for excessive water use, with the city's dam levels dropping 64 billion litres over summer, despite higher-than-normal rainfall.

Water use over summer 2017/18 was up 2.5 per cent or 33 million litres compared with the previous summer, and a dry February has made levels plummet to 65 per cent of capacity, according to Melbourne Water.

“We only need to save around six litres of water per person, per day, to get back to the target,” Melbourne Water manager Chris Williams said of the voluntary efficiency program set at 155 litres of water per person per day.