WE WRITE in response to the letter of Bernie V. Lopez titled “High manganese level in water supply” (Opinion, 5/6/16). We are issuing this clarification so that the public may be properly informed of the issue that Lopez raised pertaining to the presence of manganese in Laguna Lake, which caused temporary discoloration in the water supply of our customers in the south last April 25.
It is true that the dry spell brought on by El Niño has resulted in a sharp decline in the level of water in Laguna Lake, and this caused more sediments such as manganese and other mineral deposits at the bottom of the lake to mix with the raw water entering our treatment facility.
We have advised our affected customers of the actions that we have taken to resolve the issue—i.e., adjustments in our operations at the treatment facility and flushing of our pipelines, particularly in areas where there have been reports of water discoloration. Through these measures, we were able to resolve the water discoloration incident in less than 48 hours.
In the letter that we sent to our affected customers, we clearly stated that except for the discoloration,our water supply is still within the parameters set by the Philippine National Standards for Drinking Water (PNSDW).
Lopez’s reference to the possibility of manganese poisoning is therefore needlessly alarming.
According to the World Health Organization’s 2011 guidelines for drinking-water quality, it would require exposure to high levels of manganese over a long period before manganism develops.
Manganese forms naturally in the air, soil and water and is an essential trace element necessary for humans, plants and animals. Increased levels of manganese may affect the water’s turbidity, taste and odor but, health-wise, is not a cause for alarm. Note that under the PNSDW, manganese is classified not under “Inorganic Chemicals with Health Significance” but under “Physical and Chemical Quality for
Acceptability Aspect”—because when mixed with chlorine, it may make the water yellowish.
At a level of 0.02 mg/L, manganese will form coatings inside the pipelines that may slough off as black sediments; hence, we have cautioned our customers to cover their faucets with a clean cloth. Under the PNSDW, the permissible level of manganese in drinking water is 0.4 mg/L.
At any rate, we very much regret the inconvenience that the temporary water discoloration has caused our customers in the south. We wish to assure them that we are constantly monitoring the characteristics of the water in Laguna Lake, and we have the necessary technologies in place to continue producing water that meets the PNSDW.
—JENNIFER C. RUFO, head, Stakeholder Communications, Corporate Communications, Maynilad