Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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.

   2. A body of water, standing or flowing; a lake, river, or
      other collection of water.

            Remembering he had passed over a small water a poor
            scholar when first coming to the university, he
            kneeled.                              --Fuller.

   3. Any liquid secretion, humor, or the like, resembling
      water; esp., the urine.

   4. (Pharm.) A solution in water of a gaseous or readily
      volatile substance; as, ammonia water. --U. S. Pharm.

   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.

   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}.

   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]

   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.

   {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.

   Note: Other phrases, in which water occurs as the first
         element, will be found in alphabetical order in the
         Vocabulary.

Hard \Hard\, a. [Compar. {Harder}; superl. {Hardest}.] [{OE}.
   heard, AS. heard; akin to OS. & D. heard, G. hart, OHG.
   harti, Icel. har?r, Dan. haard, Sw. h[*a]rd, Goth. hardus,
   Gr.? strong, ?, ?, strength, and also to E. -ard, as in
   coward, drunkard, -crat, -cracy in autocrat, democracy; cf.
   Skr. kratu strength, ? to do, make. Cf. {Hardy}.]
   1. Not easily penetrated, cut, or separated into parts; not
      yielding to pressure; firm; solid; compact; -- applied to
      material bodies, and opposed to soft; as, hard wood; hard
      flesh; a hard apple.

   2. Difficult, mentally or judicially; not easily apprehended,
      decided, or resolved; as a hard problem.

            The hard causes they brought unto Moses. --Ex.
                                                  xviii. 26.

            In which are some things hard to be understood. --2
                                                  Peter iii. 16.

   3. Difficult to accomplish; full of obstacles; laborious;
      fatiguing; arduous; as, a hard task; a disease hard to
      cure.

   4. Difficult to resist or control; powerful.

            The stag was too hard for the horse.  --L'Estrange.

            A power which will be always too hard for them.
                                                  --Addison.

   5. Difficult to bear or endure; not easy to put up with or
      consent to; hence, severe; rigorous; oppressive;
      distressing; unjust; grasping; as, a hard lot; hard times;
      hard fare; a hard winter; hard conditions or terms.

            I never could drive a hard bargain.   --Burke.

   6. Difficult to please or influence; stern; unyielding;
      obdurate; unsympathetic; unfeeling; cruel; as, a hard
      master; a hard heart; hard words; a hard character.

   7. Not easy or agreeable to the taste; stiff; rigid;
      ungraceful; repelling; as, a hard style.

            Figures harder than even the marble itself.
                                                  --Dryden.

   8. Rough; acid; sour, as liquors; as, hard cider.

   9. (Pron.) Abrupt or explosive in utterance; not aspirated,
      sibilated, or pronounced with a gradual change of the
      organs from one position to another; -- said of certain
      consonants, as c in came, and g in go, as distinguished
      from the same letters in center, general, etc.

   10. Wanting softness or smoothness of utterance; harsh; as, a
       hard tone.

   11. (Painting)
       (a) Rigid in the drawing or distribution of the figures;
           formal; lacking grace of composition.
       (b) Having disagreeable and abrupt contrasts in the
           coloring or light and shade.

   {Hard cancer}, {Hard case}, etc. See under {Cancer}, {Case},
      etc.

   {Hard clam}, or {Hard-shelled clam} (Zo["o]l.), the guahog.
      

   {Hard coal}, anthracite, as distinguished from bituminous or
      soft coal.

   {Hard and fast}. (Naut.) See under {Fast}.

   {Hard finish} (Arch.), a smooth finishing coat of hard fine
      plaster applied to the surface of rough plastering.

   {Hard lines}, hardship; difficult conditions.

   {Hard money}, coin or specie, as distinguished from paper
      money.

   {Hard oyster} (Zo["o]l.), the northern native oyster. [Local,
      U. S.]

   {Hard pan}, the hard stratum of earth lying beneath the soil;
      hence, figuratively, the firm, substantial, fundamental
      part or quality of anything; as, the hard pan of
      character, of a matter in dispute, etc. See {Pan}.

   {Hard rubber}. See under {Rubber}.

   {Hard solder}. See under {Solder}.

   {Hard water}, water, which contains lime or some mineral
      substance rendering it unfit for washing. See {Hardness},
      3.

   {Hard wood}, wood of a solid or hard texture; as walnut, oak,
      ash, box, and the like, in distinction from pine, poplar,
      hemlock, etc.

   {In hard condition}, in excellent condition for racing;
      having firm muscles;-said of race horses.

   Syn: Solid; arduous; powerful; trying; unyielding; stubborn;
        stern; flinty; unfeeling; harsh; difficult; severe;
        obdurate; rigid. See {Solid}, and {Arduous}.

Source : WordNet®

hard water
     n : water that contains salts (as calcium and magnesium ions)
         that limit the formation of lather with soap