Water warning: How big a risk does the treatment failure pose to human health?

Boil notice for water from Leixlip treatment plant may continue, given risk to public

Part the Leixlip Water Treatment Plant. Photograph: Colin Keegan/Collins

Part the Leixlip Water Treatment Plant. Photograph: Colin Keegan/Collins


Treatment facilities for the bugs cryptosporidium and giardia at the Leixlip Water Treatment Plant are insufficient, according to the Environmental Protection Agency (EPA).

In an appearance at the Oireachtas Housing Committee on Tuesday, Dr Tom Ryan, director of the Office of Environmental Enforcement (OEE) at the EPA said there is currently a deficit for treatment of parasites such as cryptosporidium and giardia at the Leixlip plant.

While filter upgrade works are underway to reduce this deficit, it “will not be sufficient to confirm adequate treatment”, Ryan said in his opening statement.

His remarks suggest there may be a significant risk to public health from the diseases giardiasis and cryptosporidiosis and that the water restrictions currently affecting some 600,000 people in the greater Dublin area may have to continue for some time.

What is cryptosporidium and how does it affect humans?
Cryptosporidium is a parasite found in human and animal waste. When cryptosporidia enter the body, usually via contaminated water, they travel to the small intestine and then burrow into the walls of the intestines. The parasites are subsequently shed in faeces.

In most healthy people, cryptosporidium infection produces a bout of watery diarrhoea and the infection usually goes away within a couple of weeks. Other symptoms include loss of appetite, stomach cramps, nausea, vomiting and weight loss. The illness is most severe in small children and older people.

Patients remain infectious for between two and four weeks; parents and carers changing nappies may become infected as a result.

However in people with a poorly functioning immune system, cryptospiridosis causes a prolonged, severe and often highly debilitating illness.

Is it common?
A 2018 EPA report highlighted that cryptosporidium detection has increased in the past three years. It was detected in 25 public water supplies in 2018, up from 12 in 2016. With over 600 cases per year, Ireland has the highest cryptosporidiosis notification rate in the EU.

How is cryptosporidiosis treated?
There is no specific treatment for cryptosporidiosis; recovery usually depends on the health of your immune system. Most healthy people recover within two weeks without medical attention. If you have a compromised immune system, the illness can lead to significant malnutrition and wasting. In this case a range of antibiotics will be used in an attempt to halt the infection.

What is giardiasis?
Giardiasis is an illness caused by the giardia lamblia parasite. It occurs when the parasites are ingested, most commonly when contaminated water containing the parasites is drunk. Contaminated water may come from lakes or ponds, swimming pools, and contaminated drinking water. The bugs become encased within hard shells called cysts, which allow them to survive outside the intestines for months. Once inside a host, the cysts dissolve and the parasites are released.

What are the symptoms of giardiasis?
Diarrhoea, foul-smelling greasy stools, flatulence and nausea are the main symptoms of infection with giardia lamblia. Symptoms usually develop one to three days after exposure to the parasite. In developed countries, most cases of giardiasis occur in young children.

How is giardiasis diagnosed and treated?
Diagnosis is based on finding giardia cysts in the stool of patients. Three samples are often needed to identify the parasite. Unlike cryptosporidium, antibiotics are effective against giardia. The antibiotic of choice is metronidazole.

What is the best way to prevent these parasitic infections?
A reliable supply of clean drinking water is the most important method of prevention. Good hygiene practices such as thorough hand-washing when changing nappies also help.

While boiling water will kill both parasites, the best way to prevent human infection is to ensure our water treatment facilities are up to date and effective. Ultraviolet disinfection at water plants offers the most effective control. Unfortunately barrier methods and boil water notices will leave some bugs in our water tanks and cisterns. They offer partial prevention at best.