By Anna Cavell BBC London
Chemicals entered the river from Thames Water's works in Hertfordshire
Almost 100 people have reported feeling ill to Thames Water after the contamination of the River Lea in north-east London last month, it has emerged.
BBC London has learned that chemicals entered the river at the utility company's own sewage treatment works at Rye Meads in Hertfordshire.
The contamination is being investigated by the Drinking Water Inspectorate, the regulator of public water supplies, and any conviction would carry a fine.
In total, more than two million people were affected when the water supply to this area of London was contaminated with the chemicals 2-EDD and 2-EMD.
About 1,000 people contacted Thames Water to report foul-smelling and foul-tasting water but were told that there was no significant threat to health.
Local resident Michelle Mifka is convinced that it made her ill after she drank a glass of water on 8 February.
Michelle Mifka said she was sick within half an hour of drinking water
"I'd just gotten up, I hadn't had breakfast, I wasn't ill and I had the water," she said.
"Within half an hour I was sick, so it couldn't really have been anything else."
Thames Water said there was no evidence to suggest that pollution led to the illnesses.
In a statement, Thames Water said: "The Health Protection Agency has confirmed that the minute traces of these substances found in water from our Walthamstow works during February did not present any significant threat to the health of our customers."
Rotten eggs
This was not the first the first time these two chemicals have found their way into drinking water in England.
In April 1994 customers of Severn Trent Water reported their water as smelling like paraffin, or rotten eggs.
After receiving a number of calls from customers, Severn Trent Water decided to bring in water bowsers from elsewhere in the country, advising people not to use the water until it had identified the contaminant.
One of the district managers told a TV interviewer at the time: "The advice from the health authority is that the water is not safe to drink and we are therefore advising everybody not to drink the water at all.
"However, if people have drunk the water this morning, they may suffer an upset tummy but that's all."
Following the incident in 1994, Severn Trent Water was found guilty of supplying water unfit for human consumption in court and fined.
As a gesture of goodwill the company paid customers £25.