We’re sitting on a sea of fresh water
A look at Rarotonga’s vast underground water supply

The current drought conditions have seen many go without water for lengthy periods.
Residents are experiencing low pressure meaning water is unable to get to first floor residences or holding tanks on roofs. Residents in some areas have had no water for a week.
Times of little water raise questions about whether we should look to tapping into the underground supply.
Several years ago this paper looked into the underground water supply issue and also at whether natural springs ought to be utilized.
This issue, we take a look back at the 2008 story concerning the extent of the underground water system.
The initial story arose when the Times followed efforts by Tap Pryor in Titikaveka to source underground salt water for his oyster and fish ponds next to Titikaveka College.
At the time, Pryor was hoping to avoid forking out $15,000 to pipe salt water from the lagoon, so a decision was made to set up a drill on the property and drill down to the salt water table.
However, 30 metres down Pryor struck fresh water and an abundance of it. So much so, he began pumping it up to supply the fish tanks. Pryor said he notified the Water Division of Works. An ADB representative took a sample away for testing as to the water’s quality. This writer sampled the water and found it to be cool and very good tasting. The water was clear with no muddy or metallic taste.
Pryor discovered the pump was delivering 300 litres of cool, fresh water per minute. Based on this, Pryor estimated that around 130,000 litres per day was flowing under the property towards the beach. Pryor said it emanated from the hills and was part of a giant underground supply as yet unmeasured.
Pryor used the water then recycled it. The water was pumped up and run through the hatchery then to a large pond by his house. From there it was pumped to two new large fish tanks then back into the pond.
The pond was dug several years ago with Environment Service approval. The pond is on top of the underground fresh water lens.
Pryor said the water was suitable for drinking but it had not been tested for impurities.
Pryor’s drill created a 4 inch diameter hole and could go as deep as 75 metres.
A report for government done in 1992 by French Consultants on Rarotonga’s water resource in July 1992 included an assessment of underground water resources to determine capacity. While further research was deemed necessary, some interesting estimates were made.
The Consultants estimated that a significant amount of excess water from rainfall is seeping into the underground water table, even in the driest months of the year. This water is flowing underground towards the sea. The Consultants estimated that the 22 kilometers of flat, sandy coastal plain around Rarotonga was absorbing around 500 litres of water per second and this was flowing towards the sea. The amount being absorbed through the volcanic basement could not be calculated. They calculated that for the 32 kilometers of coastline, some 47,000 cubic metres of fresh water per day was flowing underground to the sea. For every 100 metres of beach, 5,400 litres of fresh water is flowing out into the lagoon each hour.
Back in 1992 the Consultants estimated the water demand as it might be in the year 2000. They estimated that domestic demand/tourist demand and industrial demand would be around 8,880 cubic metres a day (allowing for some leakage) and agriculture demand would be around 23,500 cubic metres a day (allowing for drought and wastage). The total demand was assessed at 32,380 cubic metres a day.
As already mentioned above, the Consultants had estimated the flow of underground water to the sea at 47,000 cubic metres a day.
Much more research remains to be done before government can consider full commercial development of the underground water supply however, it makes sense to consider some limited use say especially in times of drought.
In June 1998 SPOAC presented a technical report to government assessing the potential groundwater of Rarotonga’s coastal plain.
The report highlighted the potential for water wells to become contaminated by such items as salt water, pig waste and pollutants. A number of options were suggested such as using the water only for irrigation.
The consultants also suggested a drought management policy.
Clearly more research is required.
At the time of going to print, the Times was not able to obtain any advice from the Water Division as to future research into the underground water systems.
Next week, we will look back at the previous story on natural spring water. -Charles Pitt

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