A decade since the last severe drought and some above average annual rainfalls have taken water as a vital resource off the public radar. CHW's storages also now sit at 91.1 per cent capacity at Christmas and this reserve position is also a percentage point better than last year.

Ballarat's total water reserves are currently 55,000 megalitres which even in the worst possible scenario amounts to at least four years of use with little or no new inflows, so it appears there is little cause for concern at present.

Nevertheless water security promises to be one of the major talking points in the longer term and the memory of the period up until 2010 is forcing organisations and governments to plan for the long term.

The first issue to focus on is population increase. Already Ballarat is seen as one of the major growth centres with a projection of up to 150,000 residents by 2040 but post-pandemic 'tree changers' could also swell this number further.

Ballarat on average uses 251 ML per week or over a year, at current usage, about 13,052 ML. The CHW Annual Water Resource Summary, which notes Ballarat could more than double in size over the next 50 years, estimates this usage could increase to 15,600ML by 2040.

More critically, under higher growth scenarios this demand could grow beyond 20,000ML after 2050, a key benchmark because it is close to the figure of CHW's current supply.

But the second major factor to impact this water security is climate change and CHW has developed modeling to show a range of outcomes including more severe climate change scenarios.

The CHW report notes it is already seeing the impacts of higher temperatures, lower winter and autumn rainfall and lower stream flows on its water supply to the point where overall annual supply could potentially dip below 20,000 ML per annum over the next few years.

High-range climate change impacts of course make the issue more urgent. The point where these lines of supply and demand cross (see graph above) thus becomes the critical point for water security for Ballarat. CHW notes it is confident under both scenarios this point won't be reached before 2041.

But beyond that it also notes system improvements and extra supply will be necessary in the decades beyond to avoid a water deficit.

The great unknown in these predictions is the reduced rainfall anticipated under various climate change scenarios.

Central Highlands Water's Urban Water Strategy (UWS), which was developed in 2017, shows that one of the major factors going forward is the impacts of less rainfall in coming years.

Apart from climate variation, "as observed by historical rainfall and the long-term occurrence of extremes of drought and flood," it details the more serious impacts of increasing climate change due to greenhouse gases since 1975 and expected effects it will have in the future including lower rainfalls and higher evaporation through hotter temperatures.

With less water to go around, how will CHW look to combat the needs of a growing community? The water authority says it is already well into planning to combat any future supply issues.

"CHW have developed a number of adaptive measures to respond to drought and reduced water availability in our region, including installing groundwater bores to diversify and/or change to a more reliable water source; building pipelines to connect to water outside of our region such as the Goldfields Superpipe, making increased use of recycled wastewater, implementing ongoing water efficiency measures and when required, placing restrictions on water use."

The 'Superpipe' built to connect Ballarat and Bendigo to the Waranga Basin in the Goulburn system during the 2000-2010 drought adds flexibility to the water supply grid, allowing CHW to buy water from the irrigation systems in the state's north to supplement rainfall and storage.

Victoria's gold cities were historically founded for their alluvial assets not their abundant watercourses, so additions to the water grid - bringing water from more plentiful areas to places with high population and demand - has proved their salvation.

Increased opportunities also exist in a grid to share existing assets across the state.

For instance, in 2015 it was mooted that Ballarat could utilise a greater share of Lal Lal Resevoir, CHW's largest, of which it currently has about two thirds, by meeting Geelong's demand with water piped from Melbourne supplies and even the desalination plant in Wonthaggi under extreme scenarios.

CHW's Urban Water Strategy notes that innovation and flexibility will be key in meeting this future demand brought on by the two dependent factors but it also highlights water quality would also be crucial.

"Significant reductions in streamflow are expected over the next 50 years... although there is uncertainty on the exact magnitude and timing of the reductions," the UHW report says.

"It is essential that water quality is fit for purpose. Water quality varies between different water sources, and therefore different treatment methods and costs for producing fit-for-purpose water is required.

"Treatment methods can vary both between systems and also in different operational modes within a system - surface water may be treated differently to groundwater in the same system.

"Water quality can also be influenced by climate and inflows. For example, blue green algae was a frequent concern through the millennium drought in several of CHW's systems and during periods of low inflows some reservoirs become more salty."