Timber tanks made safe

Waimarino Bulletin, Volume 4, Issue 33, 3 February 1987, Page 7

Timber tanks made safe

Timber water tanks manufactured by New Zealand's major producer are no Ionger being roofed with arsenictreated timber. An alternative treatment based on copper naphthenate has been introduced. Copper naphthenate has very low solubility in water and can reach the tank water only by being dissolved in any moisture condensing under the roof shingles and dripping into the tank. The company supplying the copper naphthenatetreated timber asserts that one litre of condensed Water dripping into a tank at 25° C could not contain more than 0.00 15g of copper naphthenate. This means that a 70kg person would have to drink over 250,000 litres of undiluted condesate from a roof within a 24-hour period to be affected. Timber tanks built from untreated wood could require replacing within three years, whereas those of treated timber are expected to last 80 years. The Timber Preservation Authority and the Forest Research Institute were both involved in consultations during the development of Timbertank's unique construction methods in 1972.

Of more than 1000 Timbertanks constructed in New Zealand in the past 14 years, high levels of arsenic have been recorded in only six instances. Most of these were in the Gisborne area, where long dry summers had reduced water levels in the tanks. This served to concentrate any arsenic occurring either naturally in the water or through leaching. "Timbertanks are designed to preserve the natural beauty of the New Zealand landscape," says managing director of Timbertanks, M orton Jordan. "Those who buy them do so because they appreciate the need for artificial constructions to blend in with the landscape." "The change to copper naphthenate was made because of fears that arsenic could leach from the tank roof into the water supply. We stress that the previous treatment did not involve harmful levels of arsenic and fthe tanks will never constitute a danger to health," Mr Jordan says. "We were happy to switch to copper naphthenate — which is a much more expensive treatment — for the peace of mind of our clients." Timbertanks with copper naphthenate treated roofs are being used extensively by horticulturists, farmers and home owners in all areas of New Zealand.