Frequently Asked Questions: Targets for Disinfection Byproducts

Changes in organic material in our river water created levels of a disinfection byproduct that were higher than usual in one section of the city. Treated drinking water always contains some disinfection byproducts, but we monitor them closely, and if they are present at higher levels than the Environmental Protection Agency (EPA) guidelines recommend, we issue a notification.

When we issue a notification, we send a notice to homes and businesses in the affected area, and post it on our website. The notice online includes a map of the impacted area where you can search for your address and see if it is included in the notice.

Guidelines for target levels are based on the EPA’s “Lifetime Health Advisory” levels, meaning under that level, you can drink the water your entire life and it will not cause any health effects. EPA does not enforce these target levels, but the Pennsylvania Department of Environmental Protection (PA DEP) requires us to issue notifications when levels exceed those guidelines. There are no immediate health effects at those levels. Potential health effects would require drinking 2 liters of water (or 8 glasses) with elevated levels of byproducts every day for 70 years.

PWD collects and tests samples of drinking water from sixteen (16) locations throughout our distribution system every month. Target guidelines are based on the Locational Running Annual Average (LRAA) – we calculate the average of samples from each location every quarter (3 months), and then the average of the last four quarterly averages to get the LRAA. If the LRAA is higher than the guideline level, we issue a notice.

First, PWD closely monitors the levels of organic material in our source water. As levels increase, we increase the amount of powdered activated carbon (PAC) that we add. PAC allows us to remove a large amount of the organic matter in the water, thereby reducing the amount that is left to react with the chlorine.

Second, PWD closely monitors its chlorine, disinfection byproducts (DBP), and DBP precursor levels. We adjust chlorine levels throughout the water treatment process to balance the amounts needed for proper disinfection while minimizing DBP precursors and the DBPs that are formed as a result.

We’re also planning for long-term solutions. To further reduce levels of disinfection byproducts, we are planning to upgrade our drinking water treatment plants. Our Water Revitalization Plan proposes upgrades to all three of our drinking water treatment plants.

For more, go to water.phila.gov/revitalization

No, there is nothing you need to do. You do not need an alternative water source and you do not need to boil your water. You can continue to use your water as always. However, if you have a specific health concern based on any of the information provided in these FAQs, please consult your doctor.  

Disinfection is a crucial part of our water treatment process. We add chlorine to kill harmful bacteria and viruses in the water we draw from our rivers. When chlorine reacts with natural organic material in our source water, byproducts can be created. Byproducts are not the primary goal of our treatment process; they are secondary results.

The unit “mg/L” means one milligram per liter. It is equal to one part per million.

This could be compared to putting one drop of water from an eyedropper into 10 gallons of water, or two thirds of a gallon in an Olympic-sized swimming pool.

A Health Advisory Level (HAL) is an informal guideline set by the EPA. It establishes target levels for contaminants and byproducts in water. Water systems can refer to these levels when protecting public health. A Lifetime Health Advisory Level is often set to a very low amount, in this case 0.02 parts per million. By setting this target so low, scientists suggest that if people consume water over a lifetime (70 years), the low amounts won’t cause adverse human health effects.  HALs provide guidance for the water utility providers and state regulators, such as the Department of Environmental Protection (DEP), on the potential for these compounds to cause health effects to humans.

TCAA is a byproduct of disinfection. It’s the result of naturally occurring organic matter found in our source water combined with the chlorine that is added at the water treatment plant.

TCAA is not regulated as an individual contaminant. TCAA is one of a group of contaminants known as five haloacetic acids (HAA5).

The regulatory threshold, or Maximum Contaminant Level (MCL) for the combined contaminant class of HAA5 is 60 parts per billion. PWD monitors for HAA5 every month throughout the City. Compliance with the MCL is based on a running annual average at individual sampling locations. This is called a Locational Running Annual Average (LRAA).

If any individual contaminant, such as TCAA, is above the target for that byproduct, we will issue a notice that it exceeded targets, but as long as the combined running average for the HAA5 group is below the MCL, it is not considered a violation of regulations. Levels of HAA5 in Philadelphia’s drinking water are consistently lower than the regulatory threshold set by the EPA.

If the average value over the last four quarters is greater than 0.025 mg/L, which rounds to 0.03 mg/L, then we have exceeded targets as set by the EPA.