The Sembawang Hot Spring located at Gambas Avenue between Woodlands Avenue 12 and Sembawang Road, is the only natural hot spring on the main island of Singapore.It lies in a wooded area about 100 metres (330 ft) off the main road. The spring is believed by locals to have healing properties, and its water has been bottled commercially by Fraser and Neave, under the brand name of Seletaris. Since its discovery in 1909, the spring, now on land belonging to a military air base, has gone through several changes of ownership and abortive redevelopment plans. The hot spring is less frequented nowadays but remains a popular venue for weekend visitors.
During its peak, up to 1,000 people visited the hot spring at weekends. On 1 March 2002, it was closed for two months while improvement works were carried out to the area around the spring, which had become sodden and muddy. Litter had also become a problem because of the large numbers of visitors.The former dirt track leading to the spring was paved, and lined with bougainvillea bushes and high fences to protect the security of the air base. Drainage pipes were also installed. Mindef, which owns the land, allows public access between 7 am and 7 pm daily, at no charge. When the spring reopened, on 1 May 2002, more than 100 people visited the site despite the afternoon drizzle.At the same time, new free-hold condominiums were built in the surrounding area; one of the developments, built by the property arm of F&N in 2001, is called Seletaris after the company's former mineral water.
In July 2005, a Business Times reader proposed that the relevant authorities should explore the possibility of tapping the geothermal heat that lies many miles under Sembawang—similar to the project in South Australia's Cooper Basin—in order to reduce Singapore's reliance on oil and gas. The proposal was not acted upon.As of 2008, the well can still be seen locked inside a red-brick enclosure with a steel gate, and its heat can be felt outside the building. Numerous plastic chairs, pails and makeshift tubs left by visitors are stored at the perimeter of the compound, which has a makeshift shed in one corner. Caretakers manage the site to ensure its overall cleanliness, although toilets are still lacking on the premises. The hot spring is less frequented nowadays but remains popular at weekends and on public holidays, when regulars and families visit.
According to local geologists, the exact source of the spring remains unknown, but it is believed that its origin may be southwest of its actual location, possibly at Bukit Timah.Hot springs are formed when underground water comes into contact with hot rock masses. The resulting high pressure causes the water to seep upwards through cracks, forcing itself out of the ground as a spring.
A series of tests conducted by the PSB Corporation and SGS Testing & Control Services found the spring water contains 420 mg of chloride per litre, an amount which is substantially higher than the 35 to 100 mg in the water from Choa Chu Kang and Bedok waterworks. It was also found that the sulphide content is three times more than tap water and the spring water is also slightly alkaline due to the presence of minerals. This led many to believe that the spring waters have health benefits and thousands flocked to the hot spring, in a search for cures for skin conditions like psoriasis and acne, as well as debilitating ailments like rheumatism and arthritis. Although local rheumatologists conceded that hydrotherapy is an accepted treatment that can be helpful for mild forms of rheumatism or muscle strain, they, along with dermatologists, remain sceptical of claims about the healing powers of the spring water.
Water bubbles continuously in the well, releasing a slightly unpleasant sulphur odour together with steam. The temperature of the spring water is around 131 °C (270 °F).In an investigation carried out by the Nanyang Technological University in 1994, the hot spring was found to have an estimated yield of approximately 150 litres (33 imp gal; 40 US gal) per minute at ground level through installed steel casings.