How to measure the pH of water & other liquids correctly

Recently we had the following query from a customer: ' I bought some pH strips but I cannot really figure them out. I keep getting different readings for the same thing. I don't know if the brand I have is bad or if I am doing something wrong.'

Most pH test strips give a reasonably accurate reading and are simple to use. They measure the pH reliably within a very small tolerance and accurately to a level of 1 or 0.5. Bearing in mind, that pH test strips or litmus papers are not to the same accuracy ad digital testers, which will measure pH levels to 0.001.

When problems occur, they are often down to user error. Here are some key facts:

  • Temperature can influence the pH level, warmer water will have a higher pH. So all measurements should take place at the same temperature, ie room temperature. Otherwise, they can not be compared to each other.
  • Only substances that dissolve or consist of water can give you a pH (aqueous solutions). For instance, coconut oil is not water based and does not dissolve in water (it is hydrophobic), therefore it cannot have a pH.
  • Keep your hands away – our hands a source of a mix of chemicals (natural oils, lotions, soap). Do not touch the test pad of a test strip or the end of the litmus paper which you put into the solution. Do not put your hands into the solution you want to test.
  • Consider where you store your water sample – plastic tends to leach into a solution and metal can react with a solution. Ideally use clean glass, which is washed with soap thoroughly, rinsed at least 3 times in water and allowed to dry naturally.
  • You cannot test the pH of a solid and these can even interfere with the pH testing and give a false result (even tiny little undissolved particles like paint). For instance, conditioners (like hair conditioner) or soap should be dissolved in distilled/deionised  water before testing (use as little water as possible). As a general rule, it is a solution when you can see through it (because there are no particles).

 

Further Free Resources:

Got a question about water testing? Try our complete list of Free Water Testing Resources. Here are the most frequently read guides:

Disclaimer: Only opinions based upon our own personal experience or information detailed in academic journals or other publications is cited. This has been done exclusively for anyone who is interested in this subject but is not intended to replace proper analysis. We cannot accept responsibility and liability of any kind which may result from the application of this information. We always recommend to consult an expert to discuss any test results or get a full recommendation on the specific subject and specific to your situation by an expert.

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There are strict standards for the quality of drinking water within Europe mainly laid down in the EU Drinking Water Directive (98/83/EC). These are based on advice from the World Health Organisation (WHO).

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