How to test the quality of Open Water for bathing or swimming

Open Water Swimming TestThere is always a greater risk of infection or illness caused by microorganisms when swimming in open water (lakes, rivers etc) compared to a chemically treated swimming pool. This guide aims to help identify most appropriate water quality monitoring and testing (*For full details please refer to the guidelines published by the relevant authorities/bodies – our recommendations below can not replace consultation of guidelines issued by local authorities and bodies).

Testing open waters before is important to make sure that you do not put yourself or others at risk from illnesses.

The World Health Organisation (WHO) has published general guidelines. The European Union (EU) has also created a directive concerning the management of bathing water quality; it includes guidelines that all bathing water in the EU (including the UK) should meet. Swimming in inland water in the UK is regulated by the Bathing Water Regulations 1991 & 2013.
The EU directive and UK Bathing Water Regulations 1991 & 2013 are aimed primarily at those looking to offer their open water to the general public. Both are however a great source to give an insight into what is deemed acceptable water quality for people to swim in. TriathlonScotland has also published a very useful Guidance on Water Quality for Open Water Events.

Below you find a general summary of the guidelines in the United Kingdom (UK), which follows similar guidelines to the EU. In addition to this, please make sure that you always check your local guidelines to make sure that everyone is safe. If you plan to open your water to the general public you must strictly adhere to the guidelines set by the EU and UK, therefore please refer to the official guidelines*.

How often should I check the water: It is recommended to check the quality of the water regularly, ideally at the start of the bathing season, every 4 weeks, before any event, when there are visible changes to the water, after heavy rainfall as well as at the end of the bathing season. The pH should be monitored more often as it can be an early indicator of changes, because it is affected by algal and weed growth, agricultural run-off as well as waste water from industry.

How to take a water sample: With the exception of algal blooms, samples should be taken 30cm below the water surface. Samples should be transported as soon as possible after collection in a cool box (we provide a cool box as well as ice packs) so that they arrive at the laboratory on the same day.

The water quality is generally classed as excellent, good, sufficient or poor – based on the number of colony forming units per 100ml (cfu/100ml). Swimming should not take place in poor quality water. The recommendations below are based on the standards for inland water .

Parameter Value Maximum
Total Coliforms (cfu/100ml) low
Escherichia Coli (E.coli) (cfu/100ml) excellent: <500, good: <1000, sufficient: <900, poor (fail): >900
Intestinal enterococci (cfu/100ml) excellent: <200, good: <400, sufficient: <330, poor (fail): >330
pH 6 to 9
Blue-green algae (cells/ml)* If visible bloom, count should be carried out; low: <20,000; moderate: >20,000 – <100,000; high: >100,000
Conductivity The purer the water the lower the conductivity
Appearance No abnormal change in colour
Odour None
Transparency >1 metre
Surfactants No lasting foam
Mineral Oils No surface film or odour
Phenols No phenolic odour

*Please note, that not all species of blue-green algae are toxic and further investigation may be advisable where moderate levels are recorded. The Environment Agency provides species-specific values which should be looked at.

Recommended Tests for Open Water Swimming:

Laboratory Tests: To test water for public use, a laboratory test is recommended. The results of the bacteria laboratory test are available within 4-10 days and are presented in cfu/100ml. With each lab test a test report is issued. Here is a selection of relevant tests from our UKAS approved laboratory:

For the full range of laboratory tests, please click here. If you are planning on carrying out various or regular tests, then please contact us for a specific quote.

Field/Home Screening Tests: We also offer a range of field test kits which provide instant results (these are suitable for fresh water only and are screening tests). Below is a selection of products:

open water swimming tests safe swimming

Recommended Tests for Sea Water & Swimming Pools & Spas:

Sea water:

  • Field/Home Screening Teststrips: 5-in-One to test pH, Total Alkalinity, Nitrate, Nitrite and Total Hardness (these test strips can be used for fresh as well as salt water)
  • All our laboratory tests are suitable to check brackish/salty sea water. For the full range of laboratory tests, please click here.
  • Photometer: For regular self testing we can recommend the photometer test marine/salt water iDip 570 Photometer for marine/salt water.

Swimming Pools & Spas:  These guidelines are designed to give general information about regulations for open water swimming, this includes lakes, rivers etc. Different recommendations exist for swimming pools & spas – please refer to separate guidelines for these. Click here for our wide range of test strips for Pools & Spas. The iDip photometer Pool & Spa is ideal for regular testing of public pools and commcercial use. For more information about how to look after your hot tub safely and test the water regularly, click here.


Bacteria Test Strips 15 Minute for Swimming, Pool & Spa

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:

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 purchases available, please contact us to find out more.

Disclaimer: Only opinions based upon our own personal experience or information available in the public domain 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. We also recommend to check if there is any newer or later information on this subject.

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