A construction company was fined $44,500 yesterday for carrying out excavation works without approval last year and damaging a water main along the Pan-Island Expressway (PIE).

National water agency PUB said that Megastone Holdings had carried out the works on March 27 last year without an approved plan from the agency.

In the process, the company damaged a 300mm-diameter water main, resulting in a loss of 1.8 million litres of potable water, which is enough to fill three-quarters of an Olympic-size swimming pool.

It was charged under the Public Utilities Act and the Public Utilities (Protection of Water Pipes Infrastructure) Regulations.

PUB said it had to shut down the water main to carry out urgent repair works to avoid further disruption of water supply and to minimise water loss.

Water supply to airport catering company Sats Inflight Catering was disrupted for about two hours.

PUB said Megastone Holdings was conducting excavation works at a slip road from the PIE to Airport Boulevard to lay a precast drain. An underground water main was punctured when the tip of the excavator bucket hit it.

Investigations revealed that the contractor had failed to exercise due diligence during the works.

The contractor had excavated an area more than what was earlier marked out onsite.

In addition, the steel plate welded at the end of the excavator bucket to prevent puncturing of any underground pipes had dropped off during the excavation.

PUB said that the company had also failed to submit a plan to it.

This is required for excavation works that are within 10m laterally from the centre line of the 300mm-diameter water main.

The plan should be endorsed by a professional engineer and provide information on the impact assessment and methodology of carrying out the excavation works. It should also contain an instrumentation and monitoring proposal.

Since 2015, PUB has taken 34 contractors to task for damaging water mains or connecting pipes.

In its statement, PUB said it takes a serious view of acts of water wastage that could be prevented if due diligence had been exercised.

"Contractors should always refer to PUB's advisory on the prevention of damage to water pipe infrastructure before carrying out any construction works," it said.

For damaging a PUB water main or connecting pipe with a diameter of 300mm or more, offenders can be fined up to $200,000, jailed for three years, or both.

Those who carry works within the vicinity of water mains without an approved plan from PUB can be fined up to $10,000.