11Slow sand filters remove impurities mainly by:ABiological action in the top layer (schmutzdecke)BHigh pressureCBoilingDChemical reactionView AnswerDiscussWorkspaceReportSaveEasy
12An elevated service reservoir is used to:ARemove hardnessBCollect rainwater onlyCMaintain pressure and balance supply and demandDTreat waterView AnswerDiscussWorkspaceReportSaveEasy
13The grid-iron distribution system:AHas dead endsBIs only for villagesCHas interconnected pipes so water reaches points from several directionsDUses one pipeView AnswerDiscussWorkspaceReportSaveEasy
14Aeration of water removes:ABacteria completelyBHardnessCDissolved gases and tastes/odours, and oxidises iron and manganeseDTurbidity onlyView AnswerDiscussWorkspaceReportSaveEasy
15Hardness of water is caused mainly by:ADissolved oxygenBCalcium and magnesium saltsCIron onlyDSodium chlorideView AnswerDiscussWorkspaceReportSaveEasy