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水的問題---何謂硬水,何謂軟水, 兩者有咩分別
何謂硬水,何謂軟水,兩者有咩分別
硬水：水中溶解礦物質較多的水，如地下水 軟水：水中溶解礦物質較少的水，如雨水 這裡的礦物質多指鈣和鎂等離子 鹽化後易成為固體鹽（不溶於水）而名 可按鈣和鎂的含量分為不同硬度 香港的食用水屬軟水 硬水煮後能變成軟水 但經常煮硬水的水煲易長水垢（結在水煲壁的黃白色物質） 其實是水中的礦物移到水煲壁上 蒸餾後或者經離子交換樹脂過濾也可變成軟水 硬水洗衣時與簡單肥皂易長成浮渣 即不溶於水的長碳鏈酸鈣/鎂浮在水上和沾在衣物上 須浪費更多肥皂才能達到和同量軟水洗衣效果 不過目前一般清潔劑都能不受硬水影響發揮良好清潔效果 也有飲用硬水能保健 製成食品（如面食或糕點）更可口的說法
硬水是指礦物質成份高的水，軟水則是礦物質成份低的水Hardwaterthathasahighmineralcontent(waterwithalowmineralcontentisknownassoftwater).Thiscontentusuallyconsistsofhighlevelsofmetalions,mainlycalcium(Ca)andmagnesium(Mg)intheformofcarbonates,butmayincludeseveralothermetalsaswellasbicarbonatesandsulfates.Itisnotgenerallydangerous.Thesimplestwaytodetermineifwaterishardorsoftisthelather/frothtest.Ifthewaterisverysoft,soapwilltendtolatherupeasilywhenagitated,whereaswithhardwateritwillnot.Toothpastewillalsonotfrothwellinhardwater.Moreexactmethodsof'hardness'detectionuseawettitrationmethodtodeterminehardness.Totalwater'hardness'(includingbothCa2+andMg2+ions)isreportedasppmw/v(ormg/L)ofCaCO3.WaterhardnessusuallymeasuresthetotalconcentrationofCaandMg,thetwomostprevalentdivalentmetalions,althoughinsomegeographicallocationsiron,aluminium,andmanganesemayalsobepresentatelevatedlevels.CalciumusuallyentersthewaterfromeitherCaCO3,aslimestoneorchalkorfrommineraldepositsofCaSO4.Thepredominantsourceofmagnesiumisdolomite,CaMg(CO3)2.參考資料：wikipedia
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