Recharging depleted aquifers with treated sewage may be “a good idea” but much depends on the cost of the operation to determine how successful it could be, according to a former head of the Water Services Corporation.

The proposal was one of many in the water policy document published on Thursday by the Resources Ministry for public consultation.

A pilot project will soon be conducted in Gozo where excess treated sewage in the winter months will be pumped and stored in the Għajnsielem aquifer basin.

Over extraction from Malta’s ground water sources has left them depleted and at risk of drying up.

The document also suggests the wider use of treated sewage for agricultural purposes.

Former minister Michael Falzon, who was also chairman of WSC, welcomed the proposal but raised the issue of cost since water for agricultural purposes would have to be treated to a higher level than that for disposal at sea.

“The problem with distributing treated sewage to farmers for agricultural purposes was always linked to money because water had to be treated to a higher degree. The issue is who should be paying for this additional treatment, consumers through their household bills or farmers who would be using the water,” Mr Falzon said, insisting that creating a distribution network was also costly.

He pointed out that using treated sewage to recharge depleted aquifers was a good idea and a half-way solution.

“However, if the water would still have to be treated to a higher degree the issue of cost would arise once again,” he added.

Mr Falzon’s caution is grounded in reality. According to a 2006 presentation by John Mangion and Manuel Sapiano from the Malta Resources Authority, treated sewage effluent would have “to undergo polishing” before re-use either for distribution to farmers or to recharge aquifers.

The presentation was made during an EU-funded workshop in Malta that dealt with the re-use of treated sewage effluent in Malta and Sicily.

Polishing is the technical term used to describe the process by which water is treated to various levels of acceptability depending on its eventual use. It is a process also used in reverse osmosis plants to make seawater good for human consumption.

The water policy document presented by the Resources Ministry does highlight the need for studies to assess in detail the cost effectiveness of the proposals.

It says that efforts will be made to use the natural storage capacity of aquifers, particularly the perched aquifers such as the one in Għajnsielem.

However, the Malta Resources Authority is currently also examining the feasibility of creating a freshwater barrier with treated sewage to reduce the contamination of sea-level aquifers by encroaching sea water.

Other assessments include the impact on soil salinity and crops of treated sewage used for irrigation purposes.

According to a study by the National Statistics Office, agriculture used around 19.1 million cubic metres of water, mostly extracted from the ground, in one year between September 2008 and 2009.

In contrast, last year the WSC extracted only 12.7 million cubic metres of groundwater for distribution as tap water. Another 16.6 million cubic metres were ­produced by reverse osmosis plants.

Hydrologist Marco Cremona had told a conference on climate change earlier this year that unless Malta reduced its dependence on aquifers, groundwater sources may vanish in the next 15 years.

Former WSC chairman Tancred Tabone was less optimistic when he said in an interview in January that Malta would run out of ground water in “about five years”.