Mining companies are winning the support of farmers in the Dalby Downs region of North Queensland by offering to return water used during the process of coal seam gas extraction, despite concerns about the safety of the practice.

Ian Hayllor, the Chairman of the Basin Sustainability Alliance, says his group is in “preliminary negotiations” with gas companies in Queensland about the “beneficial use of produced water”.

The alliance has until now been entirely opposed to coal seam gas extraction on farms in the area, but Hayllor told Crikey that “in the past they [the mining companies] wasted the water, we’re saying for them to treat the water they pollute so it can be reused”.

Queensland Gas Company spokesman Paul Larther confirms the company has reached an agreement with SunWater, a Queensland government-owned water supply department. Under the agreement QGC will treat and then sell water used in the process of coal seam gas mining to SunWater, which will transport it to Chinchilla along a buried 20-kilometre pipeline.

SunWater spokeswoman Olga Kakourakis says the water will only be accepted by the company if it is first deemed to meet acceptable standards set by the Queensland Department of Environment and Resource Management. The department is yet to release the standards, she says.

SunWater is seeking customers along the pipeline to buy the water. It says any left over will run into the Chinchilla Weir, where it would be treated by council and eventually end up in the town’s drinking supply.

Hayllor explains water drawn from underground aquifers during the extraction of coal seam gas will be treated and then returned to the underground aquifers. The treatment will occur using a process known as “reverse osmosis”, whereby contaminated water is pumped through a membrane that then filters chemicals as they flow through.

But Crikey has discovered serious concerns exist around the effectiveness of this method for treating water used in the process of coal seam extraction. In April this year Dr Marian Lloyd-Smith and Dr Rye Senjen released a briefing paper for the National Toxics Network, which raised concerns about the effectiveness of reverse osmosis.

According to Dr Lloyd-Smith, a senior adviser to the NTN, the process is effective in capturing large molecules, but chemicals with smaller organic molecules are able to pass through the membrane with the water that is being filtered.

“Reverse osmosis has significant limitations,” she said. “Evidence shows that it will not deal with all chemical compounds inside the water and none of us can find a definitive list of which chemicals reverse osmosis will not deal with. There is certainly real concern over what it won’t pick up.”

Dr Lloyd-Smith says various membranes are used in the filtering process but due to commercial confidentiality it is usually impossible to know the exact methods used by companies engaged in the practice.

“The question is what methods of quality control are they using? It’s not that we’re opposed to the release of water but we’re opposed to the release and reuse of water that hasn’t been adequately treated … Until you’d seen studies saying that the technology these companies are using will remove all the harmful chemicals I wouldn’t be comfortable as a farmer using that water.”

Using water as a bargaining chip is the latest salvo in a long-running battle between miners and land owners over coal seam gas and the controversial practice of “fracking”. A Senate committee chaired by Liberal Bill Heffernan heard numerous complaints from farmers at hearings in Queensland this week, and probed miners on how they would clean up underground aquifers.

Wal Waldron is a committee member with the Mullaley Gas and Pipeline Accord, which represents more than 100 landowners in north-west NSW. Eastern Star Gas, which is set to be swallowed by mining giant Santos as part of an agreed takeover bid, has blueprints for a gas pipeline from Narrabri to Wellington, a plan opposed by residents because of the damage they believe will be done to valuable farming soil in the area.

Waldron says that in initial meetings the possibility of reusing water was raised but he thought using the water was “very risky” and that “there’s no way I’d want their water”.

Rosemary Nankivell, the chairwoman of the Caroona Coal Action Group, also rejects the use of recycled water. “They cannot come up with an acceptable level of water quality in my opinion,” she told Crikey.

“If it’s possible why haven’t they done it before? They’ve spent a lot of time on these water issues and haven’t been able to come up with a solution.”