The 10-million-litre tank will be an addition to the three-million-litre tank already there.

Managing director John Wilkinson said the new tank would guarantee water supply for customers for the summer. For the past five years, towns in the region have been

supplied with water from Melbourne because of continued low storage levels. Rosslynne, which is managed by Southern Rural Water, is at 4.7per cent capacity.

The new tank is part of a $20million injection for the Macedon Ranges, outlined in Western Water's corporate plan released last week.

It will spend more than $220million on infrastructure in its service area in the next five years to cater for the region's growing population and to help cope with climate change.

"This huge investment in new infrastructure will ensure we can continue to supply safe and good-tasting drinking water to all our customers, even as the expansion of Melbourne's urban growth boundary leads to a big boost in population," Mr Wilkinson said.

The organisation will spend $11million in Hume including an additional tank storage and upgrade at the Sunbury recycled water plant.

The company will upgrade Gisborne's sewage pumping station to protect Jacksons Creek from potential spills during heavy rain.

The $1.6million upgrade includes installing a high performance pump system that will reduce greenhouse gas emissions by about 11tonnes a year.

"The project includes a new 260,000-litre storage tank that will take any extra water flows on the odd occasion we have heavy rain, greatly reducing the chance of a wastewater spill into the creek," Mr Wilkinson said.