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How do pH Levels affect Water Quality?

Written by Janice M on . Posted in Water & Environmental

What is the ideal pH level of water and when it it too alkaline or too acidic?
This article explains what pH in water is and what effects the pH level will have on water quality. What options are there for measuring pH in water? The drinking water quality standards that are legislated by government require pH to be within a specified range.

What is the Meaning of pH?

The term pH derives from the French word, “pouvoir hydrogene” and means “hydrogen power”.

Definition: pH is a measurement of the concentration of hydrogen ions in a solution.

Because of its mathematical formulation, low pH values are associated with solutions with high concentrations of Hydrogen ions. High pH values occur for solutions with low concentrations of Hydrogen ions.

Simply, it can also be described as a measure of how alkaline or acidic water is.

Pure water has a pH of 7.0, and other solutions are usually described with reference to this value. Acids are defined as those solutions that have a pH of less then 7 (ie more Hydrogen ions than water); while alkalines / bases are defined as those solutions that have a pH greater than 7 (ie less Hydrogen ions than water).

For a solution to have a pH, it must contain water – thus vegetable oil and alcohol don’t have a pH.


What is the ideal Level of pH in Water?

  • Surface water systems and drinking water: 6.5 to 8.5
  • Groundwater systems is between 6 to 8.5
  • The pH level will also be an indication of whether water level is hard or soft.
    High pH water is usually hard

Water Quality Standards for pH

Waste water:

According to the Dept. of Water Affairs (DWA) Requirements for the Purification of Waste Water or Effluent Water, the pH should be 5.5 – 7.5.

Drinking water:

pH 5 to 9.7 at 25°C

View Drinking Water Standards

Effects of Low pH (Acidic) water:
  • bitter or metallic taste
  • can leave blue-green stains
  • irritates the skin, eyes and mucous membranes
  • corrodes and rusts water pipes, fittings and machinery
  • the corroded metal then enters the water, causing high levels of copper, lead and other toxic metal ions
  • these secondary metal contaminants can cause many health problems if they start to build up in large amounts
  • young fish and immature stages of aquatic insects are extremely sensitive to pH levels below 5 and many die at low pH values
Effects of High pH (Alkaline) water:
  • "hard" water with a slippery feel
  • "bicarbonate of soda" taste
  • no great risk to health and can help with acid reflux
  • difficult to get soaps to lather
  • leave mineral deposits on pipes and fittings
  • over time will decrease heating efficiency of pipes and heating elements
  • uses up more chlorine, leading to higher chemical costs for water disinfection


A small Lovibond® pen-type pH Tester

How to Measure Water pH:

The following options are commonly employed:

  • Test Strips – inexpensive option for occasional pH testing, with less accuracy required
  • Pocket Testers – small pen-type testers that have an electrode, ideal for field testing, the initial investment is higher, but less consumables are required
  • Hand-held pH Meters – highly accurate, portable, electronic testers with an electrode that can be replaced, can be multi-parameter
  • Bench-top pH Meters – ideal for frequent laboratory use
  • Photometers – this method is different from the above in that it does not have an electrode and uses a chemical reagent to measure the pH level. These electronic instruments usually measure several or many parameters and are also available in a varity of sizes: small, pocket water testers for professional swimming pool users and small business and larger multi-parameter models for comprehensive, professional water testing

We recommend that you read the article about cleaning electrodes for greater accuracy and a longer life-span of the instrument you choose.

July 2019

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