21.
The water pollution in river is measured by the dissolved amount of

22.
Ultraviolet rays can be used in water treatment as

23.
Tar roads get damaged if there is

24.
Aerated water contains

25.
The BOD values of water indicate the

26.
Iron and manganese present as pollutants in water cannot be removed by________

27.
Table salt gets moist during rainy season because

28.
The unit to measure the flow of water is

29.
When water itself combines chemically with some element or mineral it is called

30.
Sea water is saltier than rain water because