Rarotonga Now Hopeful Of

Pure Water At Low Cost

From W. H. PERCIVAL, in Rarotonga

The Cook Islands are a lot closer to solving their water supply problems as a result of a new visit by the South Pacific Commission’s public health en gineer, Mr. George L. Chan.

It was Mr. Chan’s third visit to Rarotonga and Mauke to investigate local water supplies. His first arrival was in April, 1966, when he sub mitted a report at the Government’s request. He made his second visit in June last year when he recom mended that a 30 ft long test infiltra tion gallery be built near the water intake in the Avana Valley.

This was done, and his recent visit, in late January and February, was to carry out tests at the Avana gallery.

Rarotonga’s water is untreated.

During his first visit Mr. Chan found some bacteria in the water used in Avarua, the Cook’s most densely populated area.

Mr. Chan’s task was to find a cheaper method of obtaining pure water than by treating it at the six intakes in the hills that supply an extensive system of ring and loop mains on the island.

Water gallery method

In January Mr. Chan explained the principles of the infiltration gallery to a gathering of prominent people, including the High Com missioner, Mr. L. J. Davis, the Premier, Mr. A. R. Henry and cabinet ministers.

The principles are simple. Ground water is naturally filtered when it seeps through sand, gravel, earth and rocks. This raw water is retained in a trench and is drawn off through pipes as a main supply.

Water galleries are cheap and easy to construct. The only imported material required is cement for the collection chamber and the pipes.

The galleries can be deepened or lengthened to suit the needs of ex panding populations.

Although new to Rarotonga, water galleries date back to old Mediter ranean civilisations which used them 1,000 years ago. Once built, they

need no attention, and running and maintenance costs are nil.

Mr. Chan found that the test gallery at Avana was producing be tween 125 and 150 gallons of raw water per hour per foot run. Taking the lower figure, he calculated that a gallery 335 ft long would be re quired to yield 1,000,000 gallons of water daily.

General supply

The water in the test gallery was ground water, and stream water from the Avana stream, which is 35 ft away. The tests took place after two months of unseasonably dry weather and when the stream level was very low.

Mr. Chan explained that even if the stream dried up, thus making the water intake useless, water could still be obtained from the gallery, which is 10 ft lower than the river bed.

Mr. Chan talked in an interview about the island’s present water supply. About half of Rarotonga’s 9,900 people live in houses scattered all over the island, and this causes technical difficulties such as “resist ance losses” in the miles of water pipes.

Mr. Chan said that the ring main could be balanced by dividing it into sections in such a way that the more heavily populated areas receive the greatest concentration of water. It would also be safer water, because full water pipes present less danger to health than those only partly filled. Sewage can be drawn into partly filled pipes.

He said owing to the scattered population of the island more than one water gallery might be required, but this was no real problem. Raw water is water that has not been treated in any way, but if an ad ditional safeguard was required for that obtained from the Avana gallery it could be achieved by chlorination at small cost, Mr. Chan said.

When he visited Mauke in Feb ruary Mr. Chan deepened the exist ing well there to 50 ft.

A Cook Islander, a foreman plumber, will now drill for water on Atiu Island and send reports to Mr.

Chan.