National water agency PUB plans to install more monitoring wells and sensors around Singapore so that it can better understand the groundwater system.

To do so, it will be calling two tenders over the next few months.

In a statement yesterday, the PUB said it has already been monitoring groundwater levels across western Singapore, in an area known as the Jurong Formation.

It has a network of 18 monitoring wells there. These are small holes - around 50mm in diameter - which are drilled deep into the soil to monitor water level fluctuations.

The PUB plans to install about 30 to 40 more wells in the Old Alluvium formation in eastern Singapore, as well as on Jurong Island.

While the Jurong Formation is made of sedimentary rocks, the Old Alluvium consists of sand deposits. Meanwhile, Jurong Island is land reclaimed using sand.

The PUB also plans to insert sensors into the wells to better track water level fluctuations. This will help it carry out islandwide monitoring of the groundwater situation.

"These monitoring efforts are part of PUB's groundwater studies, which are currently in the exploratory stage, involving literature review and preliminary groundwater model development," said PUB chief engineering and technology officer Harry Seah.

"Through these efforts, we hope to gain a better understanding of Singapore's geology and the presence of groundwater within the earth layers," he said.

Groundwater, which is found in spaces between soil particles and fractured rock underground, makes up about 95 per cent of the planet's useable fresh water.

In 2014, the PUB carried out exploratory studies to see if Singapore's groundwater could be extracted for use on a regular basis, or to serve as "water banks" for drought periods.

It is now working on groundwater models, and the data collected from its new efforts will help validate these models. An international panel of experts also convenes regularly to give guidance and direction to PUB's studies.