A total of 74 construction contractors were punished for discharging silty water into waterways and for providing inadequate earth control measures this year, national water agency PUB said in a statement yesterday.

While this is below the past three years' average of 100 enforcement actions each year, the agency said these errant practices can harm the environment.

Where there are excavation-type activities, known as earthworks, rain can mix with exposed earth and soil, creating a silty run-off which enters drainage systems and water bodies.

This causes an accumulation of sediment in the waterways, which reduces drainage capacity.

Currently, there are about 1,000 construction sites involved in earthworks.

Of the 74 companies cited, the agency highlighted four that were penalised this year. Two were repeat offenders - Huationg Contractor, which was fined $13,500 for four offences, and Samwoh, which was fined $10,500 for three offences.

Huationg had twice failed to provide and maintain earth control measures to the code required by PUB when carrying out earthworks, netting $3,500 in fines.

It was charged in court last month and fined $10,000 for a further two offences of not meeting the water quality requirement for the treated run-off and failing to comply with the conditions of PUB's clearance certificate.

Meanwhile, Samwoh was penalised twice for failing to meet the water quality requirement for run-off. It was fined $2,500 for an earlier infraction, and $8,000 in court last month for another instance, as well as for not complying with a PUB notice to review its earth control measures.

Two other companies, Peng Chuan Engineering Construction and Stallion Development, were found to have carried out works without a clearance certificate from PUB.

This could lead to silty water being discharged into the drainage systems, said PUB.

Peng Chuan was fined $7,800, and Stallion $7,000.

"All contractors are required to plan for and implement (earth control measures) at their sites," said the agency, adding that it conducts regular checks at these sites for any breach of earth control measures (ECM).

Depending on the stage of construction work and size of earthworks, these checks can range from fortnightly to once every two months.

PUB's chief engineer of drainage operations Choy Wai Kwong said: "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."

Singapore Contractors Asso-ciation president Kenneth Loo said his organisation has worked with the agency to produce and continually update an ECM guidebook. This is to share the best environmental practices and requirements with the industry, he added.

"Our role as contractors is vital in keeping Singapore's waterways clean and beautiful," said Mr Loo.