The Source, is the magazine of the International Water Association. The Source is received by all members of the IWA. The Authors are responsible for the choice and presentation of the facts contained in the articles and for the opinions expressed therein, which are not necessarily those of, or endorsed by the IWA and do not commit the organisation. The designations employed, the statements made and the presentation of material throughout this publication do not imply the expression of any opinion whatsoever, on the part of the IWA, or its Governing Board.