The secret life of water lies in its pH.
Have you ever turned on the tap, filled a glass, and taken a sip, only to be met with a strange metallic taste, a faint whiff of swimming pool, or even an unexpected earthiness? That experience, often dismissed as "bad water," is frequently a story of pH. This single, powerful number—a measure of how acidic or alkaline water is—acts as an invisible conductor, orchestrating the chemical reactions that determine whether your drinking water is refreshingly bland or unpleasantly tainted.
From the growth of odor-producing microbes in reservoirs to the effectiveness of treatment at your local plant, pH plays a foundational role in the sensory journey of water. This article explores the intricate dance between pH and the taste and odor of your drinking water, revealing the hidden science behind every sip.
At its core, pH is a scale from 0 to 14 that measures the concentration of hydrogen ions in water, defining its degree of acidity or alkalinity. A pH of 7 is neutral, like pure water. Values below 7 indicate acidity, while values above 7 indicate alkalinity. This is not just a linear scale; each one-unit change represents a tenfold increase or decrease in acidity 2 . This means water with a pH of 5 is ten times more acidic than water with a pH of 6.
pH < 7
Can corrode pipes and leach metals
pH = 7
Pure water is neutral
pH > 7
Can cause scaling and mineral buildup
For these reasons, the U.S. Environmental Protection Agency (EPA) recommends that public water systems maintain a pH between 6.5 and 8.5 to balance these competing factors, protecting both infrastructure and public health 1 .
When you complain about the "taste" of your water, you are often describing a combination of true taste and retronasal smell. pH influences this experience in several direct and indirect ways.
When water is too acidic, it corrodes the metal pipes it travels through. This process can release copper and lead into the water. A prominent example is lead, which even at low levels is a serious health concern and can impart a sweetish or metallic taste to water 6 . The corrosion process itself is accelerated in water with a low pH, making pH control a first line of defense for preventing metal leaching and its associated tastes 2 .
On the other end of the spectrum, highly alkaline water can have a bitter or soda-like taste. This is often associated with a high mineral content, specifically dissolved solids like calcium and magnesium (which also cause water hardness). While not typically harmful, these minerals can be perceptible and unpleasant to many consumers 6 . pH adjustment is key to bringing these minerals out of solution or preventing their dissolution in the first place.
Perhaps the most dramatic impact of pH is on the "odor" dimension of water. Two of the most common and potent odor compounds in drinking water are geosmin (GSM) and 2-methylisoborneol (2-MIB), which produce a distinctive musty or earthy smell 4 . The human nose is incredibly sensitive to these compounds, able to detect them at concentrations as low as 10 nanograms per liter .
The production of these compounds is intimately tied to pH. Key producers of GSM and 2-MIB, such as certain cyanobacteria (blue-green algae) and actinomycetes (bacteria in water and soil), thrive under specific pH conditions. Furthermore, pH determines the speciation, or chemical form, of many odorous chemicals in the environment, influencing both their volatility and how they can be removed during treatment 5 .
| Sensory Complaint | Perceived Description | Potential Cause | pH's Role |
|---|---|---|---|
| Metallic | "Coppery," "blood-like" | Corrosion of copper/lead pipes | Low pH (Acidic water) accelerates corrosion. |
| Earthy/Musty | "Dirt," "moldy" | Geosmin & 2-MIB from microbes | Influences microbial growth and compound production. |
| Chemical | "Bleach-like," "medicinal" | Chlorine disinfection byproducts | High pH can shift byproduct formation and perception. |
| Bitter | "Astringent" | High mineral content (alkalinity) | High pH (Alkaline water) is correlated with high mineral levels. |
To truly understand how pH affects taste and odor, let's delve into a key experiment detailed in the 2022 journal article, "The effect of pH on taste and odor production and control of drinking water" 5 . This study systematically investigated how pH influences the removal efficiency of geosmin and 2-MIB using a common oxidant, potassium permanganate (KMnO₄).
The experiment yielded clear and significant results. The oxidation of both geosmin and 2-MIB was most effective in a slightly acidic to neutral pH range (approximately 6.0 to 7.5). As the pH increased beyond this range into the alkaline region, the removal efficiency of both compounds dropped dramatically 5 .
For water treatment plant operators, this means that carefully controlling pH is not optional—it is essential for cost-effective odor control. Applying the same amount of expensive oxidant at a pH of 9.0 is far less effective than at a pH of 6.5.
Water treatment scientists and plant operators have a suite of chemical tools to manage pH and combat taste and odor issues.
| Reagent/Material | Primary Function | Common Use & Notes |
|---|---|---|
| Sodium Hydroxide (NaOH) | Raises pH | A strong base (caustic) used for rapid pH increase; essential for neutralizing acidic, corrosive water 2 7 . |
| Carbon Dioxide (CO₂) | Lowers pH | A safer, more controllable alternative to strong acids; lowers pH gradually without a major drop in alkalinity 2 . |
| Sulfuric Acid (H₂SO₄) | Lowers pH | A strong acid used for rapid pH reduction; requires careful handling to avoid overshooting the target 2 7 . |
| Potassium Permanganate (KMnO₄) | Oxidant | Used to pre-oxidize and break down taste and odor compounds like geosmin and MIB; effectiveness is highly pH-dependent 5 . |
| Powdered Activated Carbon (PAC) | Adsorbent | Added to water to adsorb (trap) organic molecules like geosmin and MIB on its massive surface area; a primary physical barrier against odors 4 . |
| Aluminum Sulfate (Alum) | Coagulant | Clumps tiny particles and some microbes together for removal; its performance is optimal in a specific pH range 7 . |
It is a common misconception that taste and odor are merely "aesthetic" issues. While compounds like geosmin and MIB are not considered toxic at the levels typically found in drinking water, their impact is profound . Unpleasant tap water shatters consumer confidence, leading people to believe their water is unsafe.
This perception has real-world consequences: it drives households toward expensive and environmentally damaging bottled water and erodes public trust in municipal water systems 4 6 . A loss of trust in tap water can create a psychological fear of water safety and even become a crisis for the entire drinking water industry .
Therefore, managing pH to control taste and odor is not just about creating a pleasant experience—it is a critical component of maintaining public trust in our essential water infrastructure.
From the subtle metallic tang of corrosion to the overpowering earthy smell of an algal bloom, the taste and odor of your drinking water are profoundly shaped by the invisible hand of pH. This single, powerful number influences everything from the growth of microbes in source water to the efficiency of high-tech treatment processes.
As research continues to refine our understanding, one thing remains clear: effective water treatment is a delicate balancing act, and pH is the key to maintaining that balance. The next time you take a refreshing sip of bland, odorless water, you can appreciate the complex scientific symphony that was conducted, in large part, by the careful control of pH.
Adapted from research by Adams et al., "The effect of pH on taste and odor production and control of drinking water," Journal of Water Supply: Research and Technology-AQUA (2022) 5 .