THE Commission on Audit has aired concerns about 10 out of 18 pumping stations (PS) of the Laguna Water District that tested for high levels of arsenic beyond the safe limits set by health authorities.
A 20-page Compliance Audit report released on June 26, 2025, the COA revealed that during the physico-chemical analysis conducted on February 16, 2024, there were nine long-standing pumps that failed the Arsenic concentration limit of 0.01 milligram per liter (mg/L).
The pumping stations were identified as PS 1 Bayog (0.09 mg/L), PS 3 Jubileeville (0.06 mg/L), PS 6 Lopez Heights ((0.08 mg/L), PS 7 Maahas (0.05 mg/L), PS 9 STP (0.02 mg/L), PS 11 Tranca I (0.06 mg/L), PS 12 Umali (0.05 mg/L), PS 14 Vega (0.04 mg/L), and PS 15 Villegas (0.05 mg/L).
During the retests conducted on July 16 and 18, 2024, eight of the same nine PS again failed the safety limit set by the Philippine National Standards for Drinking Water (PNSDW). The only pump that showed enough improvement to pass the parameter was PS 11 (Tranca I).
Likewise, two new pumping stations that started operations before the second test in July last year also failed with PS 17 La Village and PS 18 Tamlong showing concentrations of 0.04 mg/L and 0.03 mg/L, respectively.
The COA said the water quality test showed the Laguna Water District passed the other parameters for microbiological, physical, and chemical readings.
Auditors said the problem of high arsenic levels in the water drawn from Laguna WD’s pumps had been “a persistent issue,” which indicates that it had been tested in previous years.
They noted that both the Laguna WD and its joint venture partner, the Laguna Water District Aquatech Resources Corp (LARC) have been trying to find ways to reduce the arsenic level to a safe level, but found that they were either expensive or inefficient.
The most recent one involved the use of DMI-65 filtration, a powerful catalytic water filter that was primarily designed to remove iron and manganese in the water supply.
This was installed at the Umali and Bayog pump stations and was tested extensively from September to October 2024 and proved to be at least working as water samples showed arsenic levels in both pumps dropping to within PNSDW standards.
“However, management remains hesitant to install this in the remaining affected PS due to the feedback from other water districts that …while it is effective in the short term, its effectiveness declines over time,” the COA said.
