Pure water includes:
"...And We send down pure water from
the sky." (Al-Quran, 25:48).
"Sometime we may carry a little water
with us in the ship while at sea; if we use the water we may get thirsty.
Can we use the sea water for purification?" The Prophet said: "Its water
is pure and its carrion is lawful" (Tirmidhee)
The water mentioned above should be free of color, taste or smell. If a color, taste or smell is noticed in the water, even if these things are pure, the water cannot be used for purification.
Water which is already used for purification may be used again if it is still pure.
When water changes spontaneously as a result of salt, mud, grass and the like from lakes, it is considered pure and can be used for purification. However, if the change is due to chemical contamination, the water cannot be used for purification.
If any impurity falls in pure water and does not change its signs of purity, it may be used for purification.