DUBAI // Swimming pools and air-conditioning systems are being treated with chemicals that could allow deadly diseases to persist and even thrive in the summer, experts warn.
Many still use chlorine in liquid form, as sodium hypochlorite or calcium hypochlorite solution, rather than the safer powdered chlorine dioxide.
Chlorine cannot only fail to kill disease-causing bacteria but cause harmful side effects.
Hypochlorites react with any organic matter, especially in swimming pools or cooling systems, to form by-products, most notably carcinogenic trihalomethanes (THMs).
"Powdered chlorine dioxide is safer than [hypochlorite] chlorine in terms of generating less by-products," said Prof Walid El Shorbagy, the director of the water resources programme at UAE University.
"Chlorine has more by-products which are more hazardous."
For that reason, the chlorine dose is limited to stop it reaching the level where THMs form.
But at low doses it does not work as well as a disinfectant.
It also leaves room for more serious bacteria such as Legionella pneumophila, which causes Legionnaires disease. Legionellathrives in water and in humans is caught by inhaling its droplets.
Dormant in winter, the bacteria thrives at temperatures above 25°C, making it a hazard during summer.
And with the countless air-conditioning systems, the bug has more chance of growing in roof tanks, taps, pipes and showers.
In 2010, 80 of 100 samples from Dubai households where people had suffered unexplained health complaints tested positive for Legionella.
Chlorine dioxide can be used as a preventative measure against the bacteria.
"If the dosage of chlorine dioxide is enough, then it can definitely take care of Legionella," said Prof El Shorbagy.
"When it comes to cooling systems and fountains, it can be very useful and safer than chlorine. The UAE should really consider adopting it in the future."
But chlorine remains the disinfectant of choice for many, including the Wild Wadi Waterpark.
"Chlorine is the preferred and safest method of disinfectant for the rides at Wild Wadi Waterpark," said Gary Pogharian, its director of engineering.
"We can create what we need onsite when we need it. As long as the proper operating conditions and applications are adhered to, each will do the job well."
The Wonderland theme park still uses chlorine for its nine pools and nine slides, but plans to start testing chlorine dioxide within the next couple of months.
"Chlorine dioxide might be more expensive but it is better and safer," said Shaji Rajan, Wonderland's maintenance manager.
"Our plant is treated by Metito, [a wastewater company in Dubai], so if they switch to chlorine dioxide, then so will we."
Metito is pushing the switch on many of its clients.
"Using chlorine as a disinfectant is becoming increasingly difficult because there are many restrictions on its import, export and handling," said Bassem El Halabi, its group business development director.
"Being such an aggressive and dangerous material - chlorine gas by itself is poisonous - we had to look for alternatives."
Powdered chloride dioxide is sold as Metoxide, two powders that are mixed on-site. It avoids the harmful by-products of traditional chlorine and kills Legionella.
It can also be continuously applied at a single point in a water circuit, unlike chlorine, which has to be applied at several points to prevent microorganisms from building up throughout the whole system.
"Its handling is very easy," said Mr El Halabi. "It can be used anywhere needed for disinfection, from household to industries."
So far, its most common application is in district cooling, including chillers, coolers and cooling towers, which are the most exposed to the atmosphere and microorganisms.
"Metoxide will be very effective in treating that," said Mr El Halabi.
"It can also be used in aquaparks. It is not dangerous like normal chlorine products if swallowed."