Method of purging a liquid carrying conduit

A method of purging a liquid-carrying conduit, the method including the steps of:

• providing a hydrogel comprising an additive in form of an ion selected from a group comprising:
• chloride ions, sulphate ions, and nitrate ions;
• transporting the hydrogel along at least a portion of an offline liquid-carrying conduit to thereby purge the conduit of debris;
• removing the hydrogel from the offline liquid-carrying conduit;
• flushing the offline liquid-carrying conduit with a volume of flushing water;
• verifying removal of any residual hydrogel from the offline liquid-carrying conduit as part of a contamination risk assessment by checking the flushed water for detectable traces of the additive ion;
• characterised in that the additive ion is dissociable from the hydrogel by diffusing into the volume of flushing water to thereby enable detection of its presence within a volume of flushing water collected from the offline liquid-carrying conduit following the flushing step;
• and
• wherein, if the presence of the additive is detected following the flushing step, the method further includes repeating the step of flushing the offline liquid-carrying conduit with a further volume of flushing water;
• and repeating the verifying step until no traces of the additive ion are detected within the further volume of flushing water.