How Does pH Affect Water Quality?


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Increased pH levels cause a bitter taste to drinking water and supplies, water pipes, and other appliances become encrusted with deposits. Additionally, a high pH in water decreases the effectiveness of using chlorine as a disinfectant. On the other hand, high pH levels corrode or dissolve metals in water, increasing toxicity levels.

The potential of hydrogen (H+), or pH, is the measure of hydrogen ion activity in a solution. The pH scale ranges from 0 to 10, <7 is considered acidic and a pH >7 is considered basic or alkaline. 

The typical pH range for surface water systems is 6.5-8.6, for drinking water supplies 7.0-8.5, and for groundwater systems 6-8.5. Evaluating the pH in water is important to determine the solubility and biological availability of nutrients and heavy metals in water to determine the corrosivity. Measuring pH in water also determines whether aquatic life can utilize the environment.

Does pH Affect Water Quality?

The pH of water is a very important conventional variable of water quality, as extremely high or low pH values can be damaging to the use of water. Water that has a pH lower than 5.0 or greater than 9.6, becomes harmful for different reasons. 

Consequences Of pH Changes For Aquatic Organisms 

Elevated pH levels cause damage to the gills and skin of aquatic fish and other organisms. If levels continue to rise above a pH level of 10.0, aquatic organisms will die from ammonia poisoning. However, some fish like African cichlids can tolerate high pH levels (up to 9.5) in freshwater environments.

Low pH levels in seawater cause ocean acidification due to the reduction in calcium carbonate solubility, which corals rely on to grow their calcium carbonate skeleton. For fish, low pH levels make them more susceptible to fungal infections and other diseases. If the pH continues to decrease below 4.0, fish that cannot relocate will start to perish and die. 

Low pH levels also encourage heavy metals to dissolve in the water. When the concentration of heavy metals increases in water, the toxicity also increases. For example, increased aluminum in water can limit growth and reproduction, increasing fish mortality rates. 

Consequences Of pH Changes For Human Health

In terms of human health, higher pH doesn’t pose any health risks, however, when the pH in drinking water is greater than 8.5, it can make the water taste more bitter and contact with high-pH water can cause skin irritation. Alkaline drinking water also may neutralize acid in your bloodstream. However some people claim that alkaline water can help prevent cancer and heart disease, yet more research is needed to back these claims. 

Decreases in pH also affect the taste quality of the water. Acidic water is known to leave a metallic taste or odor to drinking water supplies, and a pH lower than 6.5 is likely to be contaminated with pollutants, making it unsafe to human consumption. 

Consequences Of pH Changes In Water Systems

To improve water quality, water is often treated with chlorine as a disinfectant. When pH levels increase, the effectiveness of chlorine as a disinfectant is reduced, therefore, more chlorine is needed to improve the quality of water. This is costly for many industries such as swimming pool centers and water purification, industrial waste, and sewage systems. 

Low pH also affects water quality, for example, metals, salts, and organic compounds are directly affected by low pH levels. In highly acidic water, some minerals dissolve in water, releasing metals and other chemical substances. Elevated pH levels also cause calcium and magnesium carbonate to build up inside water pipes and other water-using appliances. 

When the pH is low, it can also damage plumbing. This eventually leads to pinhole leaks in piping, which causes water damage to walls and can increase the number of toxic metals in water. 

Typical pH Levels In Water

pH levels can change from different water inputs such as runoff from land, groundwater, and even water draining from forest areas where weak organic acids and organic matter can alter pH levels. However, below are the typical pH levels in different water systems that are used to compare unusual pH ranges.

Type Of WaterpH Level
Drinking Water7.0-8.5
Surface Water (Streams)6.5-8.5
Groundwater 6.0-8.5

Factors That Influence The pH Of Water

Many factors can influence pH levels in the water. 

Natural Factors:

  • Calcium carbonate is the main component of limestone, which naturally buffers the water against pH fluctuations in watersheds (drainage basins)
  • Drainage basins that lack limestone are vulnerable to acid rain or mine drainage due to the lack of buffering capacity
  • Decomposing plants add acidity to the soil and often surrounding streams and lakes
  • Groundwater travels through soils, so if the soils have a high or low pH level, the pH of the water can change
  • Rainfall – natural and unpolluted rain and snowfall has a low pH of approximately 5.0-6.0, yet, when rain falls through the atmosphere, it picks up CO2 to form a weaker acid
  • During photosynthesis and respiration, aquatic plants remove CO2 which increases the pH in water – this is most common during daylight hours because aquatic plants require sunlight to photosynthesize 

Human Factors:

  • Acid rain caused by burning fossil fuels – this is not too much of an issue if the surrounding soils have a good buffering capacity
  • Increased atmospheric carbon dioxide (CO2) levels can lower the pH of water, as CO2 is very soluble in water, forming weak carbonic acid
  • Directly dumping industrial pollutants (point-source pollution) into the water can decrease the pH 
  • Mining can produce acidic runoff by exposing rocks to rainwater
  • Mining drainage can introduce acidic elements into waterways, which is an issue if the water is poorly buffered as the water can reach toxic pH levels 

Measuring pH In Water

The pH of water can be measured using colorimetric or electrochemical methods.

For highly accurate pH results, we recommend using a pH meter and probe. A pH probe measures the hydrogen-ion activity in a solution. The exchange of ions generates a voltage that is measured by the pH meter, converting the voltage into a readable pH value. 

Applications That Test The pH In Water

The most common industries and applications that use pH to test the quality of water include:

  • Wastewater treatments
  • Aquaculture and aquatic systems 
  • Drinking water treatments
  • Hydroponics (agriculture and gardening)
  • Swimming pools and spa maintenance
  • Food and beverage industry 


Increased pH levels cause bitter drinking water, encrusted water pipes, and decreased effectiveness of disinfectants like chlorine. High pH levels corrode or dissolve metals into water, increasing toxicity levels and therefore reducing the water quality. 

If you would like to know more about pH and the pH kits we have to offer, feel free to reach out to one of our staff at Atlas Scientific, part of our world-class team. We look forward to answering any questions that you may have.

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