First published on 28.08.17 in the New Scientist.

A combination of rusty water and stainless steel taps, or faucets, can put people at risk of life-threatening legionnaires’ disease.

It’s already known that rust particles in a water system, which can come from iron pipes, encourage the growth of Legionella bacteria. These bacteria cause legionnaires’ disease, which can involve headaches, muscle pain, fever and confusion. The condition has been on the rise in Europe: in 2015, there were 7000 known cases, and the European Centre for Disease Prevention and Control (ECDC) thinks there may be many more that went unreported.

Now it seems that the protective coating on stainless steel fixtures – currently a firm favourite for kitchen and bathroom sinks – can degrade over time, encouraging the growth of Legionella species.

To better understand how the material of sinks can influence legionnaires’, Wilco van der Lugt, a safety engineer who contributed to European guidelines on preventing Legionella, and his team experimented with three kinds of tap commonly found in household water systems.

The researchers tested stainless steel, brass ceramic, and brass thermostatic mixer taps, each with clean water and water contaminated with either Legionella anisa, which is the most common strain in rust in the Netherlands, or both rust and the microbe. The team monitored this set-up for more than three years.

When rust was combined with Legionella anisa in the stainless steel tap, half the water samples ended up infected. The Legionella was much better able to survive and replicate in this combination than in the set-up that involved no rust, reaching concentrations of between 20,000 and 100,000 live bacteria cells per litre.

Safer taps

This outcome could be because the film coating of stainless steel taps degrades over time if rust particles are present in the water. By the third year of testing, the concentration of bacteria in this tap had shot up.

In contrast, the brass mixer tap seemed to be the safest, with only a quarter of samples from that experiment showing contamination, even when rust was present. Van der Lugt and his team thinks that taps for sale should be explicitly tested to assess their bacteria risk.

But Victor Yu at the University of Pittsburgh, Pennsylvania, says it isn’t possible to draw conclusions about safer tap design from the work, because this hasn’t yet been linked to people actually contracting legionnaires’ disease. He also notes that a different strain of Legionella is responsible for most cases in humans.

To avoid contracting legionnaires’ disease, the ECDC recommends keeping hot-water systems heated to between 50 and 60°C, and running taps regularly to avoid water standing for too long.

Journal reference: International Journal of Hygiene and Environmental Health, DOI: 0.1016/j.ijheh.2017.08.005

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