This past week, the City of Newburyport sent a notice to residents explaining why the drinking water has a stronger‑than‑usual odor and an unpleasant taste:

“The taste and odor are related to natural conditions in the reservoirs, especially during periods of ice cover and seasonal changes in the water. These events can cause naturally occurring compounds in the water to become more noticeable. While the taste and smell may be unpleasant, this is strictly an aesthetic issue and does not pose any health risk.

The only effective way to remove this type of taste and odor is through Granular Activated Carbon (GAC) filtration. The current treatment facility does not include GAC.”— Newburyport Water Department

Why Taste & Odor Changes Happen

Newburyport’s drinking water comes from surface reservoirs. During winter ice cover, spring turnover, and rapid temperature shifts, naturally occurring organic compounds such as geosmin and MIB can become more noticeable. These compounds are harmless but can create earthy or musty tastes and odors.

How Activated Carbon Filtration Works

Activated carbon contains millions of microscopic pores that trap contaminants through adsorption — pollutants stick to the carbon surface rather than passing through. Filtration performance depends on:

• Amount of carbon

• Contact time

• Pore size and structure

• Carbon configuration (GAC vs. Carbon Block)

Activated carbon is used in two primary forms: Granular Activated Carbon (GAC) and Carbon Block (CB). Both use the same carbon media, but their performance differs significantly. Blue Ribbon Water uses Activated Carbon Block (CB) filtration.

Granular Activated Carbon (GAC)

GAC filters use coarse carbon granules loosely packed inside a cartridge. This loose bed allows for high flow rates, making GAC ideal for municipal and high‑volume applications.

Strengths

• High flow rate

• Longer service life

• Lower cost

• Effective for chlorine, taste, and odor

• Ideal for municipal and commercial systems

Weaknesses

• Lower contaminant removal

• Prone to channeling, where water bypasses carbon

• Risk of microbiological growth in stagnant pockets

• Less effective for fine particulates and short‑chain PFAS

Where GAC Excels

GAC is the preferred technology for large‑scale PFAS treatment. Properly designed GAC beds are cost‑effective and capable of reducing long‑chain PFAS (PFOA, PFOS) at municipal scale.

Carbon Block (CB)

Carbon block filters are made by grinding carbon into a fine powder and compressing it into a dense block. The carbon particles are 10–20 times smaller than those in GAC, resulting in far greater surface area and filtration performance.

Because the carbon is tightly packed, CB filters:

• Remove smaller particles and more contaminants

• Increase contact time

• Prevent channeling

• Achieve sub‑micron filtration

This structure allows CB filters to remove VOCs, pesticides, chlorine by‑products, and many PFAS compounds.

Strengths

• Highest contaminant removal

• Excellent particulate and chemical reduction

• No channeling

• Consistent performance

• Sub‑micron filtration

Weaknesses

• Lower flow rate (not noticeable in residential use)

• Shorter lifespan than GAC

Why GAC Is the Municipal Solution

The City’s notice is correct: GAC is the only effective municipal‑scale treatment for naturally occurring taste‑and‑odor compounds. It is also widely used for:

• Taste and odor control

• Organic chemical removal

• PFAS reduction

• Chlorine by‑product reduction

However, GAC is not always the best choice for homeowners.

PFAS Removal: Why It Matters

PFAS contamination is a major national concern. Municipalities rely on GAC for large‑scale PFAS treatment, but carbon block provides superior PFAS reduction at the point of use, especially for short‑chain PFAS.

When to Choose GAC

• High flow rates needed

• Large volumes of water

• Municipal PFAS compliance

• Long service life required

When to Choose Carbon Block

• Maximum contaminant removal

• Best‑tasting water

• Sub‑micron filtration

• Consistent, channel‑free performance

• Whole‑house or drinking water systems

Conclusion

GAC plays an essential role in municipal water treatment and will be included in Newburyport’s future plant. However, for homeowners seeking the cleanest, best‑tasting water, carbon block filtration provides superior performance, especially for fine particulates, VOCs, chlorine by‑products, and PFAS.

Blue Ribbon Water installs premium carbon block systems designed to deliver the healthiest, cleanest water throughout your home.

DEEPER DIVE:

What Activated Carbon Block Filters Remove:

Carbon is an extremely versatile and highly effective water treatment medium. It has immense surface area. It is the best-known treatment for organic chemicals, VOCs, pesticides, herbicides, and chlorine and its by-products. It is also an unchallenged taste-and-odor improver. Coconut shell carbon is becoming popular not only because it is made from a renewable resource but also because it produces very good   tasting water and is particularly good at trihalomethane removal. When arranged in solid carbon or extruded carbon block format, it also provides very high-quality particulate filtration, in some cases down into the sub-micron level.

Sample List of contaminants addressed by CB Filters:

• The EPA list of 32 very nasty chemical like benzene, 1,1 dichlorethylene, carbon tetrachloride, dioxin, styrene, toluene, chloroform, and vinyl chloride.

• "Total Trihalomethanes", a category made up of still uncounted chemicals, assumed to number in the thousands, that are formed when water containing organic matter (i. e., virtually all water) is treated with chlorine. The maximum allowable level for trihalomethanes, which are suspected cancer causers and are present in virtually all chlorinated tap water, is only 1/10 of one part per million.

•  The EPA's Pesticides category lists 14 familiar poisons such as Aldicarb, Chlordane, Heptachlor, and Lindane

•  The 12 Herbicides listed (2,4-D, Atrazine, etc.)

• For Organics, Pesticides, and Herbicides, the standard treatment, and in most cases the only treatment recommended, is activated carbon. Carbon is mentioned as a treatment for only one of the four Microbiological contaminants listed: turbidity.

• GAC has been shown to effectively remove certain PFAS from drinking water when it is used in a flow-through filter mode after particulates have already been removed. GAC works well on longer-chain PFAS like PFOA and PFOS, but shorter chain PFAS like Perfluorobutanesulfonic acid (PFBS) and Perfluorobutyrate (PFBA) do not adsorb as well.

• Carbon Blocks of ½ micron market remove bacteria (though manufacturers seldom make this claim) and cysts like giardia and cryptosporidium quite handily. Cryptosporidium organisms are about ten times too fat to go through the holes.

• The same is true in the Inorganic category. Activated carbon itself appears in the EPA list as a preferred treatment only for mercury, but carbon block filters can also be engineered to remove lead.

• Chlorine was not considered in the discussion above because EPA does not consider it a water contaminant. Chlorine removal is what carbon is best at, and nothing else equals carbon's ability to remove chlorine.

Timely cartridge replacement is very important, because filter carbon has different capacity for different contaminants.