Heavy Metal Encore

Nov. 12, 2013
Testing procedures for heavy metal removal certification

About the author: Mark T. Unger, CWS-VI, is technical and training manager for the Water Quality Assn. Unger can be reached at [email protected] or 630.505.0160.


Just when you thought you had read enough about heavy metal in the Unger household and heavy metals in water, I am back! Last month I discussed the various challenge waters used for testing filters that make claims for heavy metals. These challenge waters are influenced by the various water supplies across the U.S.

This month I will discuss how filters making heavy metal reduction claims are tested to ensure that they perform as expected in homes. As mentioned in the previous article, filtration products are tested at two different pH levels for each heavy metal claim requested. In addition, filtration products are tested in duplicate for each test, so a total of four products are required to be successfully tested to make one heavy metal reduction claim.

Filtration products are tested based on four pieces of information supplied by the manufacturers:

  1. 1. The heavy metal reduction claims they would like to be certified for;
  2. 2. Rated service flow rate (60 psi for plumbed-in systems) or the daily use pattern (the number of gallons or liters they would like passed through the system per day for batch treatment systems);
  3. 3. The capacity (volume of treated water over the life of the filter) they would like to be certified for; and
  4. 4. The presence of a performance indication device (PID) on the filtration system (a means of notifying the user when the filter needs to be changed or has reached or is nearing its capacity).

There are three main classifications of filtration systems that can make heavy metal reduction claims according to NSF/ANSI 53: batch treatment (pour through), plumbed-in point of use (POU), and plumbed-in point of entry (POE).

Batch Treatment Systems

Batch treatment systems treat water one batch of water at a time and typically operate by the user manually filling a reservoir in order for water to be treated. These systems are not plumbed into a pressurized supply. Batch or pour-through systems also may be called gravity filters, because the untreated water flows through the filter due to the effects of gravity. Pour-through pitchers and larger countertop carafes are examples of batch treatment systems.

For certification testing, these systems are challenged each day at the manufacturer’s recommended daily use pattern and sampled according to the requirements of NSF/ANSI 53. Batches are administered, and the filters are allowed to drain the batch into the treated water reservoir. Once the batch has been filtered, the treated water is disposed of or collected for analysis (if a sampling point occurs) and a new batch is poured for filtration.

Batch pouring continues until the manufacturer’s recommended daily use is reached. For example, a pour-through pitcher with an untreated reservoir with a holding volume of
1 liter and a daily use pattern of 2 gal per day (gpd) would require about eight 1-liter pours (7.57, to be exact) to complete daily testing.

Plumbed-In POU Systems

Plumbed-in POU systems are connected to a pressurized water supply and used to treat water at a specific location within a house (such as the kitchen or bathroom). POU systems typically have rated flow rates between 0.2 and 4 gal per minute (gpm). These systems are tested using the flow rate that results at a flowing (dynamic) pressure of 60 psi. The daily test pattern for this type of filter involves 16 hours of cycled testing and eight hours of rest under pressure.

The cycling during the testing period can be performed at 50/50 (50% flowing and 50% resting — e.g., 10 minutes flowing and 10 minutes resting) or 10/90 (10% flowing and 90% resting — e.g., two minutes flowing and 18 minutes resting) over the 16-hour test period. The cycle pattern can be requested by the manufacturer, and cycles are between 15 and 40 minutes in duration. Choosing the 10/90 cycle may be an option for systems that have limited use throughout the day and may actually improve a filter’s performance, but the test takes five times longer to complete than the 50/50 cycle.

Plumbed-In POE Systems

POE systems treat all water entering a home or building. These systems typically have rated flow rates greater than 4 gpm. Plumbed-in POE filtration systems are tested similarly to plumbed-in POU systems, with testing at 60-psi dynamic inlet pressure using a 16-hour test period with an eight-hour rest period under pressure. The main difference is that no cycling is used and the test units flow 100% of the time during the testing period. POE systems typically carry large capacities (greater than 10,000 gal), so a large amount of water is required to conduct the test.

Heavy Metal Sampling

The sampling of all filtration systems depends on the anticipated reduction capacity and whether the system has a PID. For systems with a PID or warning device, the sample schedule is initial (after 10 bed volumes of challenge water pass), 25%, 50%, 75%, 100% and 120% of the estimated capacity.

For systems without a PID, the sample schedule is initial (after 10 bed volumes of challenge water pass), 50%, 100%, 150%, 180% and 200% of the estimated capacity. Influent challenge and effluent samples (passed through each filter) are collected at each sample point and an overall percent reduction is calculated over the life of the filter.

The time it takes to test filters for heavy metal reduction varies depending on the factors mentioned above.

In conclusion, filtration systems that carry certification to NSF/ANSI 53 for one or more heavy metal reduction claim (arsenic, barium, cadmium, chromium, copper, lead, mercury and/or selenium) have undergone rigorous testing to ensure the products can provide homeowners with safe drinking water. As a homeowner, it is important to me to ensure I have done everything possible to keep my family safe, and choosing a product that has not been certified for the claims it makes does not make sense to me — maybe it will work or maybe it will not, so why risk it? It does make sense to choose a product with certified reduction claims. Keep the heavy metal on the radio and out of your drinking water!

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