Water is the essence of life. Without it we cannot go on living. In fact, the sheer volume of water on Earth is what makes this planet unique. The average person loses 3-4 liters (about 10-15 cups) of fluid a day. This may seem like a lot, but when you consider that sweat, urine, breathing and bowel movements all contribute to loss of fluids, the numbers start to make sense. Water vapor in the breath alone is responsible for 1-2 liters of water loss a day. Exercise, illness and other factors can significantly increase the rate of water loss. Losing fluid causes blood volume and blood pressure to drop. There are different forms of water sources. Pure water is very important for healthy living. Ayurveda advocates rain water as the best source of pure water.
Enlivening, satiating, comforting (healthy) to the heart (mind), refreshing, stimulating the intellect, thin of imperceptible tastes, slightly sweet, cold (coolant), easily digestable nector like in property/effect, are the properties of rain water which has fallen from the sky, coming in contact with sunlight, moonlight and wind. Its good or bad, depends chiefly on the region and season.
All other kinds of water are called sea water they should not be used for drinking except during (September-October/Autumn season). Rain water, collected in a good clean vessel and which has not become changed should be used for drinking always. In its absence, the water of the earth, which resembles rain water collected from places which are clean and vast having black or white soil and exposed to sunlight and breeze.
The water which is dirty, being mixed with slush algae weeds and leaves, which is not exposed to sunlight and wind, which is a mixture of old and fresh, which is thick, heavy (not easily digestible), frothy, containing worms, hot (by nature), causes tingling of teeth by being very cold, that rain water which is unseasonal or thought seasonal that of the first rain, (before the appearance of Agastya naksatra), that contaminated with the webs, saliva, urine, faeces of spider etc, and such other poisonous materials, should not be used for drinking.
Stated briefly, the water of the rivers which flow into the western ocean which are swift and which have pure water is good for health, where as it is opposite bad for health. The water of rivers arising from Himalaya and mountains and which get churned up well by dashing against rocks are good for health, whereas the same river if gets stagnated gives rise to worms, filariasis, diseases of the heart, throat and head.