Tap water is extensively used for primary cleaning of laboratory glassware and for cooling purpose in condensers.
Tap water if used universally in lab without further treatment can lead to erroneous results.
Unfiltered tap water can contain innumerable impurities like inorganic cations like Ca, Mg, Na, Al, Fe, Cr, Pb, etcetera, anions like chlorides, sulphates, bicarbonates, organic contaminants, low volatility organic compounds, and microbial contaminants. Traditionally highest purity waterTypeI is referred to as ultrapure water followed by ‘Type I’ and Type II in order of descending purity by ASTM. Several manufacturers provide bottled purified water to meet different analytical requirements. Of course ion exchange resin beds turn out to be favourable habitats for particles and suspended microbes which can find their way into the deionized water stream. Some info can be found easily on the web. Deionized water has similar or even higher purity than distilled water.
In the final stage exposure to UV radiation can eliminate trace organics at 185nmand inactivate microorganisms at 254nm.
Deionization is achieved by passing through a mixed cation and anion exchange resin bed. It is therefore necessary to subject the deionized water stream through filtration and activated carbon treatment to remove organic impurities. Distilled water is purified water obtained by evaporation of water and condensation of the vapour. Basically, vaporization is achieved by heating the water conventionally in a heating mantle and condensing the steam in a clean receptacle. Distilled water so obtained is commonly stored for later use. Theoretically distilled water going to be of highest purity but organic impurities having lower or similar boiling points also get carried over. It isn’t possible to use quite similar quality of water for all laboratory applications.