How to test your water supply for corrosion and scaling – How to avoid leaks and costly repair bills

Why is it important to test for corrosion and scaling? How to test for corrosion and scaling simply & quickly?

Corrosion and scaling of water can cause damage to pipes, fixtures and expensive systems. Therefore, it is worth testing the corrosiveness of a waters supply, ideally before new systems like boilers, air source heat pumps etc are installed. Once the corrosiveness and scaling ability of water has been established, filters, corrosion inhibitors, water softeners and protective coatings can be integrated – prolonging the life cycle of equipment and preventing potential leaks and water damage.

What is the difference between corrosion and scaling?

Corrosion is the gradual wearing away of metal piping caused by a chemical reaction between water and metal surface (e.g. pipes or solders). Acidic water attacks metal pipes; this can cause pinhole leaks which can be hard to detect, it can cause metal from pipes dissolving in water and causing stains on fixtures.

The opposite is the build up of limescale. Hard water, which contains high levels of minerals, can cause mineral build-up; this damages the insides of radiators, appliances (like washing machines, irons, kettles and dishwashers). Eventually it can cause blockages and slow water flow.

Corrosion and scaling damages hot water cylinders, water heating systems, air source heat pumps, boilers, water filters in properties as well as private water supplies. It can cause failures in system performance and safety and is often overlooked as a potential cause of leaks and plumbing problems. Knowing the corrosion & scaling risk of water can help inform the correct specification of filters, corrosion inhibitors (like phosphates and silicates), protective coatings, installation of a water softener and other protective components. This is useful for installers, plumber boiler service personnel and maintenance staff.

Signs of corrosion include:

  • Discoloured water: rusty, brownish, red or yellow water
  • Foul odour: a rotten egg smell from the hot water tap can be a sign of corrosive bacteria build-up inside the water heater or pipes
  • Blue/green stains on fittings & fixtures, particularly with copper pipes: often a sign of copper corrosion
  • Rust stains: reddish-brown stains on fittings & fixtures
  • Reduced water pressure or leakage: caused by corrosion debris, corrosion damage or pinhole pipe leaks
  • Flaking fixtures: greenish or white mineral deposits around faucets
  • Poor water quality: changes in taste, odour or clarity

–> Routine monitoring of water quality is essential to help prevent scaling & corrosion. Most manufacturers provide guidance regarding the recommended levels of water quality for equipment like boilers, water tanks, filtration systems, radiators, heat pumps. Test your water to establish the water quality. Discuss the test results with your installer, plumber and builder.

Below are some general suggestions regarding the preferred water quality (please also check manufacturers advice for specific equipment).

Ideally, non corrosive and non scaling tap water maintains a pH between 7.0 and 8.5 and an alkalinity (as CaCO₃) of around 40 to 200 mg/L. A combination of low alkalinity and low pH is corrosive; whilst high alkalinity and high pH cause scaling.

Water Testing: Check for corrosion & scaling – How to test water for its ability to cause corrosion and scaling

Using Water Laboratory Testing:

The Langelier Saturation Index (LSI) is a common test to determine if water is likely to be corrosive. In order to determine the LSI, our laboratory measures Total Calcium, Total Sulphur, Total Dissolved Solids (TDS), Alkalinity, Chloride, Hydrogen ion (pH) and gives a calculated LSI. How to understand the results:

LSI Level Meaning
-5 – severe corrosion treatment recommended
-3 – moderate corrosion treatment recommended
-2 – moderate corrosion treatment may be needed
-1 – mild corrosion treatment may be needed
-0.05 – none to mild corrosion probably no treatment
-0 – near balanced no treatment
0.5 – some faint coating probably no treatment
1 – mild scale coating treatment may be needed
2 – mild to moderate coating treatment may be needed
3 – moderate scale forming treatment recommended
4 – severe scale forming treatment recommended

Using Home/Field Testing – Purchase test strips to measure key indicators:

  • pH: according to the Drinking Water Guidelines tap water should have a pH between 6.5 and 9. For corrosion prevention aim for slightly alkaline water of 7 to 8 (or 8.2 to 9.5 for heating systems); for soft water, the optimum pH is 8 to 8.5. Check pH in tap water 5.5 to 9, in private water supplies 2-12.
  • Hardness: according to DWI (UK): <100ppm = soft, 100-150ppm = slightly hard, 150-200ppm = moderately hard, 200-300ppm = hard, >300ppm = very hard. Check hardness in tap water.
  • Alkalinity is the waters capacity to resist changes in pH: recommended alkalinity in drinking water is 20-200ppm as CaCO₃. Check alkalinity and pH.
  • Chloride: should be kept as low as possible as excessive levels can contribute to corrosion-related issues. According to British Drinking Water Inspectorate (DWI/ DEFRA) levels of chloride should be below 250ppm.Check levels of chloride.
  • Dissolved total metals should be as low as possible, an increased amount of metals in tap water can be a sign of corrosion. Tap water that passes through a metal pipe will read 20ppb (µg/L), Filtered or RO system-purified water should read <10ppb. Check for total dissolved metals.
  • Presence of dissolved copper, lead (test strip or laboratory testing) and iron in water can show presence of corrosion in pipes.

Next steps when corrosion or scaling have been detected

    Once a problem with water quality has been established, it is important to determine if a problem is caused by the water source (ie mains water or water from a private supply) or the plumbing system. Use a ‘First-Flush’-Test:

  • Test a water sample which has been sitting in the pipe for 6 hours.
  • Flush the pipes, then test a new & fresh water sample.
  • Compare both results.

Other Resources: How test for the cause of a leak in a house and property / How to find the cause for a leak in a house or property – click here.
Further Free Resources: Got a question about water testing? Try our complete list of Free Water Testing Resources.

If you can’t find what you are looking for then please contact us, as we can source many other test kits. Discounts for bulk purchase available, please contact us to find out more.

Disclaimer: All guidelines and recommendations accurate at time of publishing. Please check current regional / local guidelines relevant to your situation. We can not be held responsible for any information published on this webpage. The limits provided are for guidance only, we do not provide compliance statements. 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 or professional interpretation. 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.

Please note, that we can not give specific medical or water treatment advice. The above only reflects opinions. 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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