WSC reduces chemicals causing bad tap water taste

Water Services Corporation reports 30% reduction in chlorides between 2021 and 2023 and a 30% reduction in chlorine

Have you noticed that tap water tastes a bit better than usual?

Chemical parameters published in the Water Services Corporation’s annual report for 2023 suggest that it should.

This is because the average chloride content in tap water was reduced to 350 mg/l, a considerable improvement from its level of 500 mg/l in 2021. This represents a 30% reduction in three years, which comes with a reduction of chlorine content by 30% over the span of a year.

While chloride is an ion primarily affecting taste and pipe corrosion, which enters water from natural and anthropogenic sources, chlorine is a disinfectant deliberately added to water to kill pathogens, ensuring safety from microbial contamination.

The chloride content in tap water has a major influence on the taste and odour of tap water – they can impart a salty, bitter, and metallic taste and odour to the water. Moreover, elevated chloride levels can lead to the corrosion of metal pipes, contributing to the metallic taste of tap water.

And in places where water is chlorinated for disinfection, higher chloride levels can react with chlorine, potentially forming compounds like chloramines, which can have a distinctive taste and odour.

Water safety not impacted by chlorine reduction

Another important factor influencing customer acceptance of potable water is the taste and odour resulting from the disinfection processes in place.

Disinfection is traditionally done by adding chlorine. However, a disinfection optimisation exercise by the WSC has now reduced the chlorine dosage to 0.8 mg/l.

Despite the 30% reduction in chlorine levels, this had no impact on the microbiological safety of tap water, as certified by Yale University’s Environmental Performance Index, which ranked Malta among the top 10 countries in the world for the safest drinking water. The WSC now plans to further fine-tune the disinfection processes in the next few years in a way that chlorine dosing is further reduced by shifting to alternative disinfection technologies already in service at the Reverse Osmosis plant in Ħondoq, Gozo.

The WSC report does not refer to regional variations in chlorine and chloride levels - to address this problem the government has announced plans to increase the Ta’ Qali water reservoir’s capacity so that it serves as a central hub for the distribution of the tap water blend.

Record water consumption

In 2023, a record 36.8 million cubic metres of desalinated were produced by the WSC, up from 35.5 million cb.m in 2022.

Meeting water demand is possible by blending water from two sources: groundwater abstraction, and desalinated water from RO plants.

In 2023, 13.1 million cb.m – approximately 36% of potable water production – was abstracted from groundwater; 64% was produced from the four seawater RO plants, three in Malta and the recently commissioned plant in Gozo.

The balance between RO and groundwater was the same as last year. However, compared to 2017, the percentage of groundwater in the mix has been reduced from 43% to 36%.

The increase of RO water in the blend has contributed to a decrease in the salinity of tap water, because the higher the percentage of groundwater in the blend, the greater the need to treat it with chlorine to ensure it conforms to safety standards.

While the overall percentage of groundwater in the blend remained the same, the amount of groundwater abstracted from the WSC’s boreholes has increased to meet demand, from 12.7 million cb.m in 2022 to 13.1 million cb.m.

To minimise the impact of abstratcion on the Mean Sea Level aquifer, which is becoming increasingly saltier due to higher abstraction and increased sea water penetration into the aquifer, the WSC has embarked on a strategy to diversify groundwater sources by reactivating boreholes that were formerly abandoned due to collection network limitations.

With an improved network to transfer water from production sources to reservoirs, the WSC has been reactivating these abandoned sources while reducing abstraction from previously utilised sources. This results in a better distribution of groundwater abstraction, relieving stress on overutilised sources.

This spatial distribution programme kicked off in 2019, with 2023 witnessing the addition of another six refurbished sources that are now contributing to an overall improvement in the quality of abstracted water. 14 sources have been reactivated to date, with further reactivations planned in 2024.