posted by ocelli .
How can variation in hardness of water be determined in a laboratory?
How is the using of sodium carbonate disadvantageous?
There are analytical procedures that you to dtermine the harness of water. You can look most of them up on Google.
Na2CO3, sodium carbonate, often is used to "soften" water. One disdvantage is that it adds sodium ions to the water which adds to the daily intake of sodium in the body. Too much sodium intake increases the risk of health problems. That can be found on Google if you wish to read about some of the details.