Some 100 major construction sites will soon receive a checklist from national water agency PUB that could help them prevent flash flooding ahead of the monsoon season.

The list will alert contractors to keep to approved drainage plans and practise good housekeeping and safety.

PUB will be rolling out the checklist starting next week.

It also recommends that worksites take measures, such as installing closed-circuit television (CCTV) cameras to monitor construction works and establish good communication channels with the agency.

It will also intensify checks at worksites to ensure public drains around them are unobstructed.

These efforts are, in part, to avoid a repeat of the flash floods in Upper Thomson on Christmas Eve last year. PUB investigations showed that contractor Sato Kogyo had, without informing the agency, built a temporary diversion drain that was undersized at the Upper Thomson MRT station construction site.

The unauthorised drainage diversions led to flooding that cost businesses thousands of dollars.

GA Construction general manager Joseph Liew said that while the company does not have the checklist yet, many of the recommendations are already present at some, if not most, of its sites.

He noted that there are already CCTV cameras at some sites. And while they were not put up to monitor flooding specifically, he said the hardware was in place. He added that the firm would adhere to PUB's recommendations.

At a briefing yesterday, PUB said it will focus more on construction sites that have major canals running through them.

Mr Choy Wai Kwong, PUB's chief engineer for drainage operations, said 28 sites have been identified.

Major drains traverse these sites, and any blockages would result in a knock-on effect during heavy rain.

"If there is a blockage, it will disrupt the flow of more minor drains, causing floods to affect more areas," said Mr Choy.

PUB is also working with the Land Transport Authority to check critical areas such as road tunnels, vehicular underpasses and some MRT stations with flood protection barriers.

Advisories will also be sent to residents and businesses in flood-prone areas.

PUB said the public can help by staying updated on weather warnings and ensuring that they keep drains clear.

In the past three years, Singapore has averaged nine flood days a year, with rainfall levels reaching 200mm to 300mm in some places.

This is much fewer than in the past. There were 36 flood days in 2013.

This year has already seen several incidents of flash floods around the island, with four locations flooding in the past three months.

Last Thursday, heavy rain caused flash floods in Hougang that subsided after about 15 minutes.

Student Chris Wong, 24, who lives near Balmoral Road, which flooded earlier this year, said he did not know if his family had received a PUB advisory, but he makes use of the PUB app during inclement weather.

He said: "It's good to keep track because if it starts flooding, I can avoid the hassle by staying at home or keeping away from the area."