The Collaborative International Dictionary of English v.0.48:

Water \Wa"ter\ (w[add]"t[~e]r), n. [AS. w[ae]ter; akin to OS.
   watar, OFries. wetir, weter, LG. & D. water, G. wasser, OHG.
   wazzar, Icel. vatn, Sw. vatten, Dan. vand, Goth. wat[=o], O.
   Slav. & Russ. voda, Gr. 'y`dwr, Skr. udan water, ud to wet,
   and perhaps to L. unda wave. [root]137. Cf. Dropsy,
   Hydra, Otter, Wet, Whisky.]
   1. The fluid which descends from the clouds in rain, and
      which forms rivers, lakes, seas, etc. "We will drink
      water." --Shak. "Powers of fire, air, water, and earth."
      --Milton.
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   Note: Pure water consists of hydrogen and oxygen, H2O, and
         is a colorless, odorless, tasteless, transparent
         liquid, which is very slightly compressible. At its
         maximum density, 39[deg] Fahr. or 4[deg] C., it is the
         standard for specific gravities, one cubic centimeter
         weighing one gram. It freezes at 32[deg] Fahr. or
         0[deg] C. and boils at 212[deg] Fahr. or 100[deg] C.
         (see Ice, Steam). It is the most important natural
         solvent, and is frequently impregnated with foreign
         matter which is mostly removed by distillation; hence,
         rain water is nearly pure. It is an important
         ingredient in the tissue of animals and plants, the
         human body containing about two thirds its weight of
         water.
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   2. A body of water, standing or flowing; a lake, river, or
      other collection of water.
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            Remembering he had passed over a small water a poor
            scholar when first coming to the university, he
            kneeled.                              --Fuller.
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   3. Any liquid secretion, humor, or the like, resembling
      water; esp., the urine.
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   4. (Pharm.) A solution in water of a gaseous or readily
      volatile substance; as, ammonia water. --U. S. Pharm.
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   5. The limpidity and luster of a precious stone, especially a
      diamond; as, a diamond of the first water, that is,
      perfectly pure and transparent. Hence, of the first water,
      that is, of the first excellence.
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   6. A wavy, lustrous pattern or decoration such as is imparted
      to linen, silk, metals, etc. See Water, v. t., 3,
      Damask, v. t., and Damaskeen.
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   7. An addition to the shares representing the capital of a
      stock company so that the aggregate par value of the
      shares is increased while their value for investment is
      diminished, or "diluted." [Brokers' Cant]
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   Note: Water is often used adjectively and in the formation of
         many self-explaining compounds; as, water drainage;
         water gauge, or water-gauge; waterfowl, water-fowl, or
         water fowl; water-beaten; water-borne, water-circled,
         water-girdled, water-rocked, etc.
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   Hard water. See under Hard.

   Inch of water, a unit of measure of quantity of water,
      being the quantity which will flow through an orifice one
      inch square, or a circular orifice one inch in diameter,
      in a vertical surface, under a stated constant head; also
      called miner's inch, and water inch. The shape of the
      orifice and the head vary in different localities. In the
      Western United States, for hydraulic mining, the standard
      aperture is square and the head from 4 to 9 inches above
      its center. In Europe, for experimental hydraulics, the
      orifice is usually round and the head from 1/2 of an inch
      to 1 inch above its top.

   Mineral water, waters which are so impregnated with foreign
      ingredients, such as gaseous, sulphureous, and saline
      substances, as to give them medicinal properties, or a
      particular flavor or temperature.

   Soft water, water not impregnated with lime or mineral
      salts.

   To hold water. See under Hold, v. t.

   To keep one's head above water, to keep afloat; fig., to
      avoid failure or sinking in the struggles of life.
      [Colloq.]

   To make water.
      (a) To pass urine. --Swift.
      (b) (Naut.) To admit water; to leak.

   Water of crystallization (Chem.), the water combined with
      many salts in their crystalline form. This water is
      loosely, but, nevertheless, chemically, combined, for it
      is held in fixed and definite amount for each substance
      containing it. Thus, while pure copper sulphate, CuSO4,
      is a white amorphous substance, blue vitriol, the
      crystallized form, CuSO4.5H2O, contains five molecules
      of water of crystallization.

   Water on the brain (Med.), hydrocephalus.

   Water on the chest (Med.), hydrothorax.
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   Note: Other phrases, in which water occurs as the first
         element, will be found in alphabetical order in the
         Vocabulary.
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WordNet (r) 3.0 (2006):

soft water
    n 1: water that is not hard (does not contain mineral salts that
         interfere with the formation of lather with soap) [ant:
         hard water]