Should preferably be done during installation, particularly work which will be concealed. Pre-assembled units can be tested where made and inspected on delivery and/or before fi xing. Final tests should be applied on completion of the installation both for soundness and performance. Air or smoke test should be used generally, but, if water be used, then the ‘test’ should be up to the level of the lowest sanitary appliance. The water test should be used for new systems only. With old systems incorporating shallow seals, the pressure must be limited accordingly. Any defects revealed should be made good and tested again, until acceptable. Water seal also serves to indicate whether seal is effective or not.