HoTWater
River pollution monitoring for Henley-on-Thames.
HoTWater
River pollution monitoring for Henley-on-Thames.
Unlike designated bathing sites, Henley-on-Thames does not have designated bathing status, meaning environmental agencies do not routinely monitor water quality in this section of the river.
In designated bathing areas, water quality is monitored regularly during the bathing season to help the public assess the risks of entering the water. These tests measure bacteria including E.coli, with results reported in colony-forming units per 100ml ( cfu/100ml ).
Environmental agencies classify water quality into the following categories:
🟢 Excellent – EC: ≤500 cfu/100ml
🟡 Sufficient – EC: ≤900 cfu/100ml
🔴 Poor – EC: >900 cfu/100ml (i.e. Worse than Sufficient)
If water quality is rated Poor, authorities advise against swimming.
Since no official monitoring exists for Henley-on-Thames, local volunteers test river water at multiple sites on this stretch of the river. These tests use a Fluidion Alert 1 analyser ** to asses the water samples taken from the Thames (See Certification note below).
During 2025 water samples were taken at four sites: two on Tuesdays and the other two on Thursdays. Test results were then typically published the following day, once analysis was complete.
While we apply DEFRA classifications to our results for reference, it’s important to note that official classifications are based on seasonal data, not single samples. DEFRA classifications also involve tests for Intestinal Enterococci. (See Understanding DEFRA data)
Please note that like the EA testing these tests do not include the sediment in the river which can contain E.coli, etc.
It should also be noted that the DEFRA classifications refer to results from laboratory tests that follow DEFRA standards, whereas the results displayed on this website and in the HoTWater app come from a Fluidion ALERT 1 analyser, which provides for more rapid results. However, the Fluidion ALERT 1 results are often higher than the DEFRA results because they can also detect particle-associated E.coli that DEFRA methods may miss.
The River Thames in this area receives wastewater from treatment plants in Reading, Wargrave, and Henley and the river flows through residential, commercial, and agricultural zones. Many individuals, clubs, and organisations are concerned about water quality and the lack of up-to-date official data to guide their activities on the river.
The HoTWater app and associated data aim to bridge this information gap, helping river users make more informed decisions about their water-based activities.
About HoTWater
The HoTWater group is a volunteer organisation passionate about wild swimming, paddleboarding, and boating. We are concerned about water quality at Henley-on-Thames and the lack of up-to-date information. In collaboration with other organisations, we conduct water quality tests at various locations on the River Thames.
The testing locations are:
Fawley Meadows (2025 only)
Water Testing Disclaimer
The HoTWater group conducts tests for various water quality indicators and pathogens, including E. coli. These tests are performed in good faith; however, neither the HoTWater group, its volunteers, nor any affiliated organisations can be held liable for:
• Errors in conducting or processing tests
• Delays in obtaining or publishing test results
• Any reliance on the information provided
Limitations of Liability
The HoTWater app and website share test results to help river users make informed decisions. However, these results are only a general guide and may not reflect real-time conditions. By using our app, data or website, you acknowledge that:
• The HoTWater group, its volunteers, and affiliated organisations are not liable for any harm or damage suffered due to reliance on our data.
• The information is provided without guarantees, conditions, or warranties regarding accuracy.
• We exclude all liability to the fullest extent permitted by law for actions taken or not taken based on our content.
User Responsibility
All users of the River Thames must assess the risks before entering the water or engaging in recreational activities. Water quality can change rapidly, and test results may not reflect current conditions.
Third-Party Links & Data
Our app data and website may reference third-party organisations or external data sources. We are not responsible for the accuracy, availability, or reliability of external information.
Changes to These Terms
We reserve the right to update these Terms and Conditions. Continued use of our app or website constitutes acceptance of any changes.
Effective Date: 16/June/2025
HoTWater respects your privacy. The HoTWater app does not collect, store, or share any personal data.
Information We Collect
We do not collect any personal information from the HoTWater app.
Third-Party Services
We use Firebase Analytics to collect anonymous data about how the app is used (e.g., how often it is run). This helps us understand usage trends to improve the app.
No personally identifiable information is collected, stored, or shared. We do not use advertising or track users across other apps or websites.
Changes to This Policy
If there are any changes to this privacy policy, we will update this page.
Certification
** The HoTWater group are certified under the Fluidion Water Safety Excellence Certification Program
Known issues with the HoTWater app
A number of features in the HoTWater app, including the scrolling of results, may not work as expected on older versions of iOS/iPadOS.
The HoTWater app version 3.0 and later (Sepember 2025) will not run on iOS/iPadOS versions earlier than 18.0
External links
Water Testing River Thames (for pollution readings from other sites)
Wallingford Beach (Environment Agency)
Contact Us
For further information email: romaine.dapples.4i@icloud.comff