Taste and odour

Taste and odour problems

Taste and odour problems can be caused by household plumbing - here's how to fix it. 

TCP-like tastes are difficult to investigate as they often occur intermittently. They are most often related to internal plumbing and pipework - particularly plastic hoses.  

What causes it?  

The most frequent cause is the hose connecting the mains supply to a washing machine or dishwasher. These flexible hoses can release small amounts of phenolic compounds.  

When these mix with chlorine already in the water, these compounds react to create chlorinated phenols which give a TCP-like taste to the water.  

How to test an appliance  

The quickest and easiest way to identify if an appliance is causing the taste problem is, when the appliance is not in use, turn off the water supply to the appliance using the service valve at the point where the hose connects to the mains supply. Please ensure that the appliance is not in use.  

With this valve closed, water from inside the hose cannot get back into the supply that feeds your tap so the taste should disappear.  

How to solve the problem  

Closing this valve is a temporary fix as opening the valve will cause the issue to return.  

To fix the problem, you can either:  

  • replace the flexible hose on the appliance ensuring it is an approved part (please refer to the manufacturer for advice as replacement parts can be difficult to find). You can also check the WRAS approved products directory  
  • install a check valve between the mains supply pipe and the appliance hose. This valve only allows water to travel into the hose, preventing the backflow of any water from the hose, into the drinking water supply. Check valves can be bought from most plumbing merchants and DIY stores but please ensure the product is approved for use with drinking water - see WRAS approved products directory.  

This diagram shows the cross section of an internal spring component of a check valve:  

Check valve cross section

This simple diagram demonstrates the check valves that need to be installed on a washing machine or dishwasher hose.

Washing machine check valves


Single check valve
This is a typical single check valve
Isolation valve
This is an example of a washing machine/dishwasher isolation valve with built in check valve