pure substances and mixtures

Pure water (100% water, without any other substances) is a kind of pure substances. However, when the concentration of water in the solution is not 100%, we call such solution a mixture.

i.e. Even a solution containing 99.9% of water and 0.1% othere substances such as sodium chloride (commonly known as table salt), this solution is still a mixture.

it depends on what is your requirement.
usually, pure water is treated as high quality water .

111111111111111111