PUB has penalised 74 civil and building contractors in 2017 for discharging silty water into the waterways, and for providing poor earth control measures (ECM) at their sites, the national water agency said on Tuesday.

Silty water is generated when rainwater runoff mixes with exposed earth materials and soil at construction sites. Therefore, contractors are required to implement certain measures to separate silt from the water they use, before discharging it into the public drains.

When not removed from construction discharge, silt will build up in the waterways.

"This will affect waterways' effectiveness in channelling stormwater flow and also the environmental aesthetics," PUB said.

In the last three years, PUB has on average taken enforcement action against 100 contractors for failing to comply with ECM requirements. Offenders can be fined up to S$5,000 for each offence of silty water discharge, and S$50,000 for inadequate ECM.

Peng Chuan Engineering Construction Pte Ltd and Stallion Development Pte Ltd were two out of the 74 contractors convicted. According to PUB, both firms carried out works which could lead to discharge of silty water into the drainage system, without obtaining a clearance certificate from the water agency. Peng Chuan Engineering Construction and Stallion Development were fined S$7,800 and S$7,000 respectively.

PUB added that recalcitrant offenders included Huationg Contractor Pte Ltd and Samwoh Corporation Pte Ltd.

Huationg was fined a total of S$13,500 for four ECM offences. It was fined S$3,500 earlier this year for its "failure to provide ECM in accordance with the Code of Practice on Surface Water Drainage when carrying out earthworks", PUB said. Subsequently in November, it was charged in court and fined S$10,000 for "two offences of not meeting the water quality requirement for the treated runoff, and failing to comply with the conditions of the clearance certificate".

Samwoh Corporation was fined a total of S$10,500 for three ECM offences. It was fined S$2,500 earlier this year for failing the water quality requirement for the treated runoff. It was also charged in court last month, and fined S$8,000 for two offences of "failing to comply with a notice to review their ECM, and not meeting the water quality requirement for the treated runoff".

Said PUB's chief engineer, Choy Wai Kwong: "Two-thirds of Singapore is water catchment. Silty discharge into the drains and canals will result in accumulation of sediments and affect drainage capacity."

He added: "Also, to protect our source of water supply, all of us should play our part in keeping our waterways clean. It is important to adopt a co-ownership approach where PUB works closely with the construction industry to build industry competencies and maintain high ECM standards."

PUB noted that before the start of earth works, contractors must engage qualified Erosion Control Professionals to design an ECM plan, obtain a clearance certificate from PUB, and implement the necessary measures on site. The ECM will include erosion control to minimise bare earth surfaces; and sediment control to collect, store and treat silty water generated during a rain event.