Sewer – Discharge of effluent into. A mixed liquid fell within the definition of trade effluent in s 141(1) of the Water Industry Act 1991. It was to be treated as a single mixture, and not separated into what had been its former parts. Accordingly, the Court of Appeal, Civil Division, dismissed Boots UK Ltd's appeal against the lower court's ruling that the respondent water and sewerage services company had been entitled to levy metered charges on the whole of the mixed liquid in question, which included trade effluent from Boots UK Ltd's factory and surface water.