Democratic Party lawmaker Helena Wong has said that outdated and incorrect guidelines may have been the cause of copper residue being discovered in drinking water at some Hong Kong housing estates.

Wong said she reviewed teaching materials for workers from multiple industry sources and found that they incorrectly told workers to apply flux or resin – a paste used to solder pipe joints – on the inside of pipes.

Helena Wong flux resin copper pipe
Helena Wong; Flux or resin inside copper pipe. Photo: HKFP.

She said the UK’s Water Regulations Advisory Scheme, issued years ago, stated that the paste should not be applied to the inside of pipes. The strongly acidic chemical – with a pH value of 1-1.5 – can cause corrosion of copper pipework, leading to a blue discolouration of water owing to the high levels of copper. Only a thin layer should be applied outside the pipes, the guidelines state.

Blue substances – copper oxide – have been discovered at Kai Ching Estate, Lower Ngau Tau Kok Estate and Hung Hom Estate – all of which had pipes replaced after being affected by the 2015 lead-in-water scandal.

Long-term consumption of copper oxide may cause damage to the kidneys and liver.

Copper oxide water tap
Copper oxide in sand filter of water tap. Photo: HKFP.

Wong found that the Reference Materials on Connecting Copper Pipes – published by the Construction Industry Council Hong Kong in March last year – along with a a teaching video compiled by the City University of Hong Kong and the Hong Kong Housing Society, both wrongly instructed workers to apply the paste to the inside and outside of piping.

“I am very shocked by this,” Wong said. “This might be a careless mistake. But if this is given by a professional body, I don’t think we can accept this kind of misunderstanding. They should have the professional judgment to teach the workers what is the proper way.”

The paste has been in use for more than a decade and incorrect usage may have affected many housing estates, according to experienced plumbers Wong spoke to.

Wong said the Water Supplies Department had told her the excess use of paste was likely the cause of the incident, but she added that the department may not understand that the issue could be caused by applying the paste inside pipes.

copper pipes
Diagram showing incorrect procedure in Reference Materials on Connecting Copper Pipes. Photo: Screenshot.

“I don’t blame the workers,” Wong said. She added that the Water Supplies Department should have verified the proper method and alerted the industry.

Wong also said she was not certain whether workers had enough protective gear when applying the paste, since it is a poisonous material.

The teaching video showing incorrect procedure:

YouTube video

Wong presented a jar of Fernox Powerflow Flux to the press. A spokesperson for Fernox said that the product was not poisonous and “is designed and independently approved to be used with potable water and has been [used] for decades in Hong Kong, UK and Europe.”

Wong said the government should consider waiving a month of water fees for estates previously affected by the lead-in-water scandal.

Kris Cheng is a Hong Kong journalist with an interest in local politics. His work has been featured in Washington Post, Public Radio International, Hong Kong Economic Times and others. He has a BSSc in Sociology from the Chinese University of Hong Kong. Kris is HKFP's Editorial Director.