What is "inch of water"

Inch \Inch\, n. [OE. inche, unche, AS. ynce, L. uncia the twelfth part, inch, ounce. See Ounce a weight.]

1. A measure of length, the twelfth part of a foot, commonly subdivided into halves, quarters, eights, sixteenths, etc., as among mechanics. It was also formerly divided into twelve parts, called lines, and originally into three parts, called barleycorns, its length supposed to have been determined from three grains of barley placed end to end lengthwise. It is also sometimes called a prime ('), composed of twelve seconds (''), as in the duodecimal system of arithmetic.

   12 seconds ('') make 1 inch or prime. 12 inches or primes (') make 1 foot.
   --B. Greenleaf.

   Note: The meter, the accepted scientific standard of length, equals 39.37 inches; the inch is equal to

2. 54 centimeters. See Metric system, and Meter.

   2. A small distance or degree, whether of time or space; hence, a critical moment; also used metaphorically of minor concessins in bargaining; as, he won't give an inch; give him an inch and he'll take a mile.

   Beldame, I think we watched you at an inch.
   --Shak.

   By inches, by slow degrees, gradually.

   Inch of candle. See under Candle.

   Inches of pressure, usually, the pressure indicated by so many inches of a mercury column, as on a steam gauge.

   Inch of water. See under Water.

   Miner's inch, (Hydraulic Mining), a unit for the measurement of water. See Inch of water, under Water.

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. To make water.

   1. To pass urine.
      --Swift.

   2. (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.

Inches of water, wc, inch water column (inch WC), inAq, Aq, or in is a non- SI unit for pressure. The units are by convention and due to the historical measurement of certain pressure differentials. It is used for measuring small pressure differences across an orifice, or in a pipeline or shaft. Inches of water can be converted to a pressure unit using the formula for pressure head. An inch of water column (iwc) is synonymous with an inch of water gauge (iwg).

It is defined as the pressure exerted by a column of water of 1 inch in height at defined conditions. For example, 39 °F (4 °C) at the standard acceleration of gravity; 1 inAq is approximately equal to 249 pascals at 0 °C.

Alternative standard conditions in uncommon usage are 60 °F, or 68 °F (20 °C), and depends on industry standards rather than on international standards.

In North America, air and other industrial gasses are often measured in inches of water when at low pressure. This is in contrast to inches of mercury or psi for larger pressures. One usage is in the measurement of air ("wind") that supplies a pipe organ and is referred simply as inches. It is also used in natural gas distribution for measuring utilization pressure (U.P., i.e. the residential point of use) which is typically between 6 and 7 inches WC (6~7" WC) or about 0.25 psi.

1 inAq ≈ .036 psi, or 27.7 inAq ≈ 1 psi.

:{| |- |1 inHO ||= 248.84 pascals (60 °F) |- |rowspan=7| |= 2.4884 mbar or hectopascals (60 °F) |- |= 2.54 cmHO (4 °C) |- |≈ 0.0024558598569 atm |- |≈ 1.86645349124 torr or mmHg (0 °C) |- |≈ 0.0734824209149 inHg (0 °C) |- |≈ 0.0360911906567 PSI |}