SINGAPORE - Singapore's consumer watchdog has found that reusable plastic water bottles here are generally safe to use.

Mystery shoppers from the Consumers Association of Singapore (Case) bought 20 different brands of reusable plastic bottles from supermarkets, neighbourhood retail outlets and outdoor shops here.

Two samples of each bottle - from lesser-known brands and costing between $2.50 for a 400ml bottle and $30 for a foldable 1.5-litre bottle - were set to a laboratory to test for Bisphenol A (BPA), a carbon-based synthetic compound used to make certain plastics.

BPA-based plastic is clear and tough, making it a popular choice for consumer goods such as water bottles, compact discs and can linings.

There have been health concerns related to human exposure to BPA.

The test of the 20 bottles - 11 carrying "BPA-free" claims and nine without - involved filling the bottles with distilled water and keeping them at a constant temperature of 40 deg C for 24 hours. The water was then tested for BPA.

According to the test results, the polycarbonate bottle made by Zenxin, a Chinese manufacturer, released 0.08 micrograms of BPA per millilitre of water - well within the European Union's (EU) BPA migration limit.

The Agri-Food & Veterinary Authority of Singapore (AVA), the regulator of food-contact items like reusable water bottles, adopts the EU's BPA migration limit of 0.6 micrograms per ml of test stimulant.

A recent study by the University of Exeter in England suggested a positive relationship between high urinary BPA levels and heart problems and diabetes in humans.

Past studies on animals also show that very high doses of BPA were likely to affect the liver and kidneys.

The AVA does not prohibit the use of BPA in the manufacturing of food containers, including infant feeding bottles.

Correction note: An earlier version of this story said the AVA prohibits the use of BPA in infant feeding bottles. The AVA does not prohibit the use of BPA in food-grade containers.