Water Quality InformationWritten By Actual Experts


Fluoride and Tap Water: What You Need To Know

Analies Dyjak @ Monday, July 25, 2016 at 1:14 pm -0400

Eric Roy, Ph.D.  |  Scientific Founder

Since starting Hydroviv, the most heated questions that our support team receive often deal with the issue of fluoride in tap water, mostly due to the conflicting "information" found on the web. There are a lot of different factors that contribute to the “Fluoride Controversy” and the goal of this article is to lay out some historical context and give a non-exhaustive summary of the credible science.

Fluoride and Dental History:

The origin of fluoride in tap water can be traced back to the early 1900’s when a young dentist named Frederick McKay moved to Colorado Springs to open his first dental practice. One of his first observations upon arriving to Colorado Springs was that a large portion of the local population had unexplained heavy brown stains on their teeth. While the discolored teeth were unsightly, McKay also observed that they were unusually resistant to decay, and set out to figure out the cause. In 1931, after decades of persistent investigation, McKay and his collaborators discovered that the discoloration and resistance to decay were due to unusually high concentrations of fluoride in the local water supply. 

In the 1930’s, water testing methodologies became more sophisticated, which allowed researchers to investigate whether or not there was an "ideal" fluoride concentration in water that was high enough to prevent tooth decay, but not so high that it would cause the unsightly discoloration (also known as mottling). One set of researchers found that a fluoride concentration near one part per million (ppm) seemed to be the “sweet spot” that satisfied both requirements. Fast forward to 1945, and Grand Rapids, MI became the first city to add fluoride to their public water supply with the goal of improving dental health. The measure worked, and cavities in children born after the start of fluoridation dropped by more than 60%. Seventy years later, fluoride remains a major tool used by dentists and the public to combat tooth decay.

While this is certainly a success story, a lot has been learned about dental fluoride treatment since the mid 20th century. For example, we have learned that most of the protection provided by fluoride appears to be topical (a result of the fluoride coming in contact with the tooth itself after it emerges from the gums), rather than sub gum line tooth growth. This means that the anti-decay benefits can be realized by applying it topically (e.g. using toothpaste, mouthwash).

Is Ingesting Fluoride Bad?

While there is near consensus among public health and dental organizations that the population-scale dental benefits of fluoride in tap water outweigh the risks, The World Health Organization, Center for Disease Control, and other organizations agree that some children in North America are getting too much accumulated exposure to fluoride, which can lead to a condition called fluorosis. Although nearly all cases of fluorosis in North America are purely cosmetic, they are problems nonetheless, which has generated discussion about lowering the "ideal" concentration of fluoride in drinking water and/or decreasing the amount of fluoride in children’s toothpaste formulations.

In addition to the problems associated with fluorosis, there is concern among some that fluoride can affect neurological development and function in children. There are, in fact, human studies (mostly Chinese & Indian populations) that have found a correlation between high fluoride exposure and lower IQ. In 2012, a group from The Harvard School of Public Health conducted a meta-analysis (i.e. combining the results of different studies) of all available data, and concluded that “The results support the possibility of an adverse effect of high fluoride exposure on children’s neurological development.” As you might imagine, this conclusion obviously generated a great deal of alarm when framed by the media, and was cited by opponents of fluoridation as proof that adding fluoride to tap water is dangerous. However, when you read the actual study, the group from Harvard also wrote in the same article that each of the original studies “had deficiencies, often very serious ones that limit the conclusions that can be drawn.” Furthermore, when the same authors were interviewed at a later time by the news media, they were quick to point out that the study was not directly applicable to drinking water fluoridation in the US, because the original studies included some subjects from areas where natural fluoride concentrations in drinking water were more than 10 times higher than the concentrations found in North American fluoridated tap water. They argued that a more relevant study would compare subjects whose drinking water had no fluoride to subjects whose water had fluoride levels at or near levels found in fluoridated North American tap water. The ideal study would also use a subject population where other factors that contribute to IQ (e.g. poverty, lead, arsenic) are well-controlled. Since 2012, more studies (with varying research goals) on the topic have been conducted, and the methodologies, results, and conclusions continue to be passionately debated in the context of tap water fluoridation in North America.

Even more recently, tap water fluoridation has been brought forward when a British scientist published the first observational study showing a population-level association between fluoridated tap water and hypothyroidism. However, this study is less than one year old, so it is too recent to follow-on studies or peer-reviewed debate play out in the scientific literature. This is a "stay tuned" situation.

Overall Takeaway on “The Fluoride Controversy”

As we step back from the history and science of tap water fluoridation, we must remember that a number of factors go into shaping public policy, for example balancing individual choice against benefits to the overall population. Proponents of tap water fluoridation are adamant that the dental benefits outweigh the potential health risks, particularly for low income families who may not have access to dental care or products. However, others argue that because dental hygiene and products have improved (e.g. fluoride toothpastes, mouthwash), there is no longer a need to accept any risk associated with ingesting fluoride in drinking water. Still others believe that it is fundamentally inappropriate for municipalities to administer widespread fluoride medical treatments through public water supplies.

Overall, it’s a situation when there are multiple different (but reasonable) viewpoints on the topic, which can be extremely frustrating for anyone who is seeking a definitive black or white answer to guide their lifestyle. It also generates an opportunity for people to present misleading (or fabricated) "data" to sway public opinion. (Just remember, anyone can make a website). If individuals who use fluoride toothpaste and mouthwash decide to purchase a water filter that reduces their exposure to ingested fluoride, we make sure that they are not doing it in response to something they read about government-sponsored public poisoning programs, the "fact" that drinking fluoridated tap water is the same thing as drinking sarin, or out of fear that the reason why tap water fluoridation was invented was to find a profitable use for toxic waste. While those claims would certainly help us sell a lot of custom water filters, they simply are not true.

As always, feel free to drop an email to [email protected].


Other Articles We Think You'll Enjoy:
Tap Water Chlorination: The Good, The Bad, The Unknown
Does Boiling Or Freezing My Water Remove Lead?
Does New York City Have A Lead Problem?

Tech Talk: A Very Close Look at How Water Filters Work

Analies Dyjak @ Monday, July 25, 2016 at 1:21 pm -0400
Eric Roy, Ph.D.  |  Scientific Founder
It seems that there is some confusion about how water filtration works, and I think it is partially due to the use of the word “filter”.  In this article, we try to clear up to the confusion with a Scanning Electron Microscope!

The word "filter" conjures up images of things like coffee filters or other things that catch particles, but a better way to think about water filtration media is as a 3-dimensional material that water flows through, a structure that better resembles a sponge.  An even better way to think about filtration media within a system is as a stack of these individual sponge-like “stages”, where each stage removes a different contaminant, until it becomes saturated.  Much like how a soaked sponge cannot mop up any more water, a saturated water filter stage doesn't "soak up" any chemicals that it was designed to remove.  This is why it is critical that any water filter used in your home has enough capacity to filter out the chemicals that you are asking it to, and that you change the cartridges before they become saturated.

The concept of "saturating a filter" is best demonstrated using  Scanning Electron Microscope (SEM) images of two different types of filtration media.   These images were collected as part of a product life cycle failure test, where we intentionally pushed the filtration system beyond its useful life.  
Water filtration media scanning electron microscopescanning electron microscope image of filtration media
The first set of images show two types of pristine filtration media before it has processed any water.  For Filtration Media Type I, the structure is 3 dimensional and  web-like, while Media Type II has a high surface area granular structure.  The two filtration media  have different microstructures because they perform different jobs in the purification system.
SEM Imgae of water filtration media
The second set of images shows SEM scans for the same two filtration media types, near the end of the cartridge's useful life.  For the Type I media, you can clearly see the particulate and colloidal contaminants trapped in the web-like structure, which is exactly how the stage is supposed to perform.  In the image of Type II Media, the previously sharp and angular looking media has formed a visible layer of contaminant "fuzz" that it has pulled from the water.   At this point in the filter's life cycle, the stages are approaching saturation, and it's time to get a new cartridge.
This final set of SEM images show what both media types look like once they've been used well beyond the useful lifetime.  If a filter cartridge is fully saturated like this, it provides absolutely no protection against target contaminants.  This is what happens when you don't replace your filter cartridge!

Pretty Neat Eh?

As always, feel free to leave water filter technology or water related questions/comments in the comments section, or send your thoughts to [email protected].

​Have a great day!

Other Great Articles From Water Smarts Magazine:
Tap Water Chlorination: The Good, The Bad, The Unknown
Fluoride in Municipal Tap Water: What You Need To Know
​Disinfection Byproducts: What You Need To Know

Should I Use A Shower Filter?

Analies Dyjak @ Monday, July 25, 2016 at 1:29 pm -0400
...my skin irritation was caused by being hypersensitive to chloramine in DC's tap water...and learned that a number of my friends...used shower water filters because they had similar issues with city water.

Tech Talk: Water Filter Stages

Analies Dyjak @ Monday, July 25, 2016 at 1:31 pm -0400
When people do their research on water filters, the topic of "stages" often comes up.  Water filter manufacturers try to use this spec to convince you to buy their product, but do you really know what  it means?

Simply put:  The number of “stages” refers to the number of things done to purify water within a filtration system.  Some examples of water filter stages include size exclusion filters, granulated activated carbon, ion exchange … things like that.   In theory, each water filter stage is present to improve the water’s quality.

With that said, It makes some sense that you would want the maximum number of stages to really clean up your water, right?

Sometimes Yes.  Sometimes No.  

If all stages are doing something useful… then “the more, the better”... but unnecessary or ineffective stages just slow down your filter's flow rate and drive up the price of the multi-stage water filter!

Because Hydroviv's Shower Filters are designed to handle "tough tap water"  we use 4 stages of filtration.  We use graduated size exclusion stages, and multiple stages that use advanced sorbent materials.

If your multi-stage water filter doesn't catch the particles, your faucet's aerator certainly will!

The purpose of  size exclusion is to catch tiny particles that would otherwise "gum up" or interfere with the sorbent materials, or could clog up your shower head or sink's aerator (see picture).  The sorbent materials are responsible for removing impurities from the water.   The end result is a highly advanced shower purification system that purifies the toughest tap water, and doesn't slow down your shower's flow rate!  

A lot of people are asking "stage-related" questions about our upcoming drinking water purification system.  Let's just say... that we can't talk about it until the patent is filed... (Can you tell that we are excited?)

If you have any questions about water filter stages (or anything else), feel free to leave a comment or email [email protected].

Tap Water Chlorination: The good, the bad, the unknown

Analies Dyjak @ Monday, July 25, 2016 at 1:36 pm -0400
Eric Roy, Ph.D.  |  Scientific Founder
We get asked about tap water disinfection using a lot. Here's the good, the bad, and what we are still learning about various aspects of chlorine in tap water.

The Good:

Shortly after scientists in the 1800's demonstrated that microorganisms are responsible for many diseases, people began experimenting with ways to disinfect water. Fast forward to 1908, Jersey City began injecting chlorine into the public tap water supply, which marked the beginning of large-scale water disinfection in the United States. Since then, disinfection practices have become commonplace in the developed world,  and the spread of waterborne illness through public water supplies has come to a screeching halt. This is a very good thing.

The Bad:

By design, chlorine-based disinfectants (like bleach) cause damage to living things, otherwise they wouldn’t be effective. Of course, chlorine-based compounds don't kill humans at concentrations found in tap water, but there are known side effects of consuming and showering in chlorinated water, including skin,eye & stomach irritation. While the allowable chlorine levels set by EPA are at a level low enough so they don’t cause adverse effects in the majority of people, some people (myself included) are sensitive to chlorine-based chemicals found at concentrations allowed in tap water.

In addition to these negative “health based” side effects, there are other “nuisances” caused by chlorine in water. For example, anyone who has spent time in a chlorinated pool or hot tub knows that chlorine-based chemicals can cause hair and clothes to fade (picture below), and a quick Google search reveals plenty of reasons for using purified water for things like watering houseplants, watering gardens, and filling fish tanks.
Dedicated hot tub swimsuit. You can clearly see where the waterline is!

It's safe to say that in an ideal world, we wouldn’t need to disinfect our drinking water with chemicals  to make it safe. However, until we find a "magic disinfection wand" that can operate economically on the municipal scale, individual households must use water purification systems if they want to remove chlorine-based chemicals from water used for drinking, bathing, washing food, cooking, watering, etc.  

The Unknown

Here's what we know:
  • We know that untreated water can transmit waterborne diseases (e.g. dysentery, Cholera, E. coli …) 
  • We know that disinfecting water with chlorine-based chemicals greatly minimizes this risk.  
  • We know that the known side effects of chlorine-based disinfectants are minor when compared to the risk of waterborne disease. 

However, as is the case with most things, our understanding of water quality is still progressing. A great deal of research is currently focused on a class of chemicals referred to as "disinfection byproducts." Simply put, disinfection byproducts are the chemicals that form in water when chlorine-based disinfectants react with organic matter. 

Scientists are still studying the chemistry and toxicology of these compounds, but what we do know suggests that these chemicals may not be great for us over the long term. 


About 25% of municipalities  in the US (including Washington, DC) use chloramines (also known as combined chlorine) as the primary public water supply disinfectant. Chloramines are formed by adding ammonia to chlorinated water. Chloramines (like chlorine) is an effective disinfectant, and it's effect is persistent in the distribution system due to its low volatility. However, this persistence makes it so chloramines do not "go away" if you leave an unsealed container in the fridge overnight, so we have to deal with the associated taste and odor.


DC's tap water switches over to a chlorine disinfection cycle for a few weeks each spring. This more aggressive "spring cleaning" kills any microbial buildup that may have occurred throughout the distribution system. During these few weeks, many DC residents may notice a change in their tap water's taste and odor. Fortunately, because chlorine is more volatile than chloramine, the unpleasant taste/odor is minimized if you let a container of water sit out overnight.


Other Great Articles From Water Smarts Magazine:
Fluoride in Municipal Tap Water:  What You Need to Know

Lead Contamination in Flint, MI Drinking Water:  Why it Could Happen in Your City?