The NSW Government is to fast-track housing developments for a Sydney population increase of nearly two million people despite a lack of new water sources.

Sustainable Australia Party spokesman Kelvin Thomson said development planners had failed to take into account the water shortage.

'That level of population growth for Sydney is not sustainable,' he told Daily Mail Australia on Saturday.

'State and Federal governments need to look at the role of migration as the driver of population growth.'

A crowded train platform in Sydney where infrastructure is under pressure from rapid migration-driven population growth. The NSW Government says another 1.9 million people are to be added by 2041

The population of Greater Sydney is forecast to rise to 7.1 million people over the next 21 years, according to NSW Government population projection figures updated earlier this month, with more than half of the growth coming from migration.

Sydney had a population of 5.2 million people as of June 2018 according to the Australian Bureau of Statistics, making it an increase of 1.9 million people.

The state as a whole is expected to grow on average by over 100,000 people each year until 2041, the updated figures said.

Each person uses an average of 183 litres of water per day, down from 195 litres per person in 2018-19, Sydney Water said.

Sydney residents are now on water restrictions with dam levels below 45 percent due to drought.

The extra 1.9 million people projected would create additional demand of 347.7 million litres of water per day.

Each year they would need 126.9 gigalitres of fresh water, which is more than one fifth the size of Sydney Harbour - which holds 500 gigalitres of water.

There are no new major sources of water for the Greater Sydney region and the $2.3 billion desalination plant is already running at full capacity, providing 250 million litres of drinking water per day or about 15 percent of supply.

To cope with rapid migration-driven population growth, the NSW Government's Metropolitan Water Plan promotes recycling sewage, greywater and storm water for watering gardens.

Sydney's $2.3 billion desalination plant is at full capacity, dam levels are less than 45 percent full and residents are on water restrictions. There are no new water sources in Sydney to provide 126.9 gigalitres per year of water for the population increase. Recycling is the plan

New housing developments will be fitted with a separate plumbing system to deliver treated and recycled sewage unfit for drinking through purple-coloured pipes and taps for use on gardens and for flushing toilets, a Sydney Water spokesperson told Daily Mail Australia.

The Metropolitan Water Plan also talks about cutting people's water usage through 'demand management'.

Restricting new dwelling approvals to reduce population inflows has not been mentioned.

The NSW Government last month announced it would revise planning regulations in a move that would instead fast-track major housing developments to cater to increased population growth.

Rapidly built high-rise apartment blocks have provided housing for the influx of new residents

The reform push would 'slash assessment times, reduce red tape, and fast track projects in high growth areas', NSW Planning Minister Rob Stokes and Premier Gladys Berejiklian jointly told the Committee for the Economic Development of Australia (CEDA) NSW State of the State event in November.

NSW planning minister Rob Stokes has promised to stream-line more developments

The Planning Institute of Australia said the reforms would simplify the planning system to cut red tape, reduce assessment timeframes and 'supercharge' new development hubs across New South Wales.

Drought-stricken country New South Wales areas are also now suffering from water shortages.

Mr Thomson said the NSW Government changes would make it easier for property developers to fast-track new housing developments.

'Whenever you see them 'reducing red tape' it's code for taking away the say of local communities to make it easier for property developers to get what they want.

'Sydney is subject to over-development and we don't agree with changes to the planning rules that advantage property developers at the expense of residents.'

Daily Mail Australia contacted Mr Stokes' office via telephone and the online contact form but did not receive a reply in time for publication.

Daily Mail Australia has contacted Ms Berejiklian's office several times via email and Twitter to ask why more development is being approved at a time of water shortages but has not received a reply.

According to the Sydney Planning Panels third quarter Dashboard Report, $2.58 billion worth of developments were approved in the September quarter of 2019 including 932 new dwellings.