Local MP Alan Mak has written to Environment Secretary Steve Reed to express his concerns over plans for water recycling at the new Havant Thicket reservoir.
Mr Mak said he was seeking urgent clarification of Mr Reed's intentions and position following the Labour Minister's recent visit to the reservoir site.
A report on the visit in The News said that Mr Reed had given his 'seal of approval' to both the reservoir and water recycling.
Although the reservoir is already under construction, Mr Reed is yet to make a final decision on the additional water recycling plan.
The reservoir is being built by Portsmouth Water in partnership with Southern Water. Southern Water is now also seeking permission for what it calls the Hampshire Water Transfer and Water Recycling Project.
This would involve treated wastewater from Budds Farm Wastewater Treatment Works being used to top up the new reservoir.
Mr Mak said: "There are still a number of important legally-required regulatory and planning application stages for the water recycling project to go through, and I am concerned that Mr Reed's remarks as Secretary of State compromise the integrity of these processes and prejudge their outcomes.
"Portsmouth Water has a good local reputation and there are no concerns about the quality of its water supply at present.
"In contrast Southern Water does not command the confidence of consumers, and there are widespread doubts about its competence to build and administer the Water Transfer and Water Recycling Project."
He added: "This is in any case a technology which is not proven in the UK, considerable concerns exist about it, and the security and integrity of the water supply is a matter of the utmost importance.
"To date neither Labour’s Environment Secretary nor the water companies have been able to provide reassurance to consumers that it is a reliable source of supply."
Mr Mak said he recognised the importance of reducing the need to abstract water from our precious chalk rivers and aquifers, but that Mr Reed was on course to undermine public confidence in the water supply.
He said: "We need measures which reduce waste and inefficiency, make better use of our existing natural sources, and build confidence in the capability of the water industry.
"I urge the Labour Government to engage with the concerns of local residents before proceeding any further with any water recycling project including Southern Water’s proposal."
Mr Mak, East Hampshire MP Damian Hinds and Fareham and Waterlooville MP Suella Braverman have united to oppose the water recycling plan.
They say there is a lack of confidence in Southern Water to operate the scheme, especially as the technology is unproven in the UK.
The MPs are urging residents to make their views known by taking part in Southern Water's online public consultation on the water recycling plan before it ends on April 4. Go to https://www.hampshirewtwrp.co.uk/consultation.html
Mr Mak has also launched a petition calling on the Environment Secretary to refuse Southern Water's water recycling proposal. To sign, go to https://www.alanmak.org.uk/WaterRecycling
