Ultra-low TDS water may not mean healthier water: PCRWR expert
ISLAMABAD – The growing use of Reverse Osmosis (RO) systems in households is prompting water quality experts to caution consumers against unnecessarily removing minerals from drinking water and treating an extremely low Total Dissolved Solids (TDS) concentration as a sign of superior water quality.
In an interview with APP, Director, National Water Quality Laboratory, Pakistan Council of Research in Water Resources (PCRWR), Saiqa Imran, said RO systems were useful where water contained excessive dissolved salts or specific contaminants requiring treatment, but their unnecessary use could remove naturally occurring minerals from otherwise acceptable water.
She said a TDS concentration below 100 milligrams per litre, particularly concentration of 20, 30 or even 14 milligrams per litre, should not automatically be considered ideal drinking water.
“People often assume that if the TDS concentration is very low, the water is safe and better. This is not correct,” she said.
According to her, reverse osmosis removes dissolved substances, including mineral salts, from water. Therefore, where the source water already meets the relevant quality standards and is free from harmful chemical and microbial contamination, unnecessary RO treatment may not be required.
She said water with TDS levels in the range of around 300 to 500 milligrams per litre could provide a more desirable mineral content, while the national drinking water standard permits TDS up to 1,000 milligrams per litre.
For bottled water, she said the applicable TDS standard was 500 milligrams per litre. Saiqa Imran explained that TDS levels naturally varied from region to region because of differences in geology and water sources.
Water in Islamabad, for instance, generally had TDS levels of around 300 to 600 milligrams per litre, while freshwater sources in mountainous areas such as Hunza could have levels of around 200 milligrams per litre.
In contrast, groundwater in parts of South Punjab could have substantially higher TDS, while levels in the Cholistan region could reach around 25000 to 30000 milligrams per litre, she said.
She stressed that the appropriate treatment depended on the actual quality of the source water rather than simply its TDS concentration.
“If the natural water is within the required limits and has no chemical or microbial contamination, treating it unnecessarily through RO is not the best approach,” she said.
The expert further highlighted that bottled water producers commonly use RO treatment and may subsequently add selected minerals to the treated water.
She urged consumers to have their source water tested before installing an RO system and to ensure that filtration systems were properly maintained and adjusted according to water quality requirements.
She said the objective should be to remove harmful contaminants while retaining appropriate mineral content rather than simply achieving the lowest possible TDS concentration.
