1. Water

2.  Naturally occurring water exerts its solvent effect on most substances it contacts. So its impure, containing varying amounts of dissolved inorganic salts along with dissolved and undissolved organic matter and microorganisms.

3. Drinking water  Contain less than 0.1% of total solids, determined by evaporating a 100-mL sample to dryness and weighing the residue (which weighs <100 mg).  It must meet the U.S. Public Health Service regulations with respect to bacteriologic purity.

4.  Acceptable drinking water should be: 1- clear. 2- colorless. 3- odorless. 4- neutral or only slightly acidic or alkaline.

5.  Ordinary drinking water from the tap is not acceptable for the manufacture of most aqueous pharmaceutical preparations because of the possible chemical incompatibilities between dissolved solids and the medicinal agents being added.  Signs of such incompatibilities are precipitation, discoloration, and occasionally effervescence.

6.  Its use is permitted in:  Washing.  extraction of crude vegetable drugs.  Preparation of certain products for external use.

7. Purified Water, USP  Purifi ed Water, USP, is obtained by distillation,ion exchange treatment, reverse osmosis, or other suitable process.  It is prepared from water complying with the federal Environmental Protection Agency with respect to drinking water.

8.  Purified Water, USP, has fewer solid impurities than ordinary drinking water. When evaporated to dryness, it must not yield more than 0.001% of residue (1 mg of solids per 100 mL of water).  Purified water has only 1% as much dissolved solids as tap water.

9.  Purified Water, USP, is intended for use in the preparation of aqueous dosage forms except those intended for parenteral administration (injections).  The main methods used in the preparation of purified water are distillation, ion exchange, and reverse osmosis; these methods are described briefly next.

10. Distillation Method  Many stills in various sizes and styles with capacities ranging from about 0.5 to 100 gallons of distillate per hour are available to prepare purified water.  Generally, the first portion of aqueous distillate (about the first 10% to 20%) must be discarded because it contains many foreign volatile substances usually found in urban drinking water

11.  Also, the last portion of water (about 10% of the original volume of water) remaining in the distillation apparatus must be discarded because distillation to dryness would undoubtedly result in decomposition of the remaining solid impurities to volatile substances that would distill and contaminate the previously collected portion of distillate.

12. Ion Exchange Method  ion exchange for the preparation of purified water offers a number of advantages over distillation.  For one thing, the requirement of heat is eliminated and with it, the costly and troublesome maintenance frequently encountered in the operation of the more complex distillation apparatus.

13.  The ion exchange equipment in use today generally passes water through a column of cation and anion exchangers consisting of water insoluble synthetic polymerized phenolic, carboxylic, amino, or sulfonated resins of high molecular weight.

14.  These resins are mainly of two types:  1- the cations, or acid exchangers, which permit the exchange of the cations in solution (in the tap water) with hydrogen ion from the resin.  2- the anions, or base exchange resins, which permit the removal of anions.

15.  M+ indicating the metal or cation (as Na+) and the X− indicating the anion (as Cl−).

16.  Water purifi ed in this manner, referred to as demineralized or deionized water, may be used in any pharmaceutical preparation or prescription calling for distilled water.

17. Reverse Osmosis  osmosis is the flow of water through a semipermeable membrane from a less concentrated solution to a more concentrated solution.  the flow in RO is cross-flow system (from a more concentrated to a less concentrated solution); thus the term reverse osmosis.

20.  a pressurized stream of water is passed parallel to the inner side of a filter membrane core.  A portion of the feed water, or influent, permeates the membrane as filtrate, while the balance of the water sweeps tangentially along the membrane to exit the system without being filtered.

21.  The filtered portion is called the permeate because it has permeated the membrane. The water that has passed through the system is called the concentrate because it contains the concentrated contaminants rejected by the membrane.

22.  Depending on their pore size, cross-flow filter membranes can remove particles defined in the range of  microfiltration (0.1 to 2 μm, e.g., bacteria).  ultrafiltration (0.01 to 0.1 μm, e.g., virus).  Nanofiltration (0.001 to 0.01 μm, e.g., organic compounds in the molecular weight range of 300 to 1,000).  reverse osmosis (particles less than 0.001 μm).  Reverse osmosis removes virtually all viruses, bacteria, pyrogens, and organic molecules and 90% to 99% of ions

23. water for injection, USP  This water is purified by distillation or by reverse osmosis and meets the same standards for the presence of total solids as does Purified Water, USP. and may not contain added substances.  Although water for injection is not required to be sterile, it must be pyrogen free.  The water is intended to be used in the manufacture of injectable products to be sterilized after preparation.

24. Sterile water for injection, USP  Packaged in single-dose containers not larger than 1 L.  It must be pyrogen free but does have an allowable endotoxin level, not more than 0.25 USP endotoxin units per milliliter.  it may not contain any antimicrobial agent or other added substance.  This water may contain slightly more total solids than water for injection because of the leaching of solids from the glass-lined tanks during sterilization.

25.  This water is intended to be used as a solvent, vehicle, or diluent for already sterilized and packaged injectable medications.

26. Bacteriostatic water for injection, USP  sterile water for injection containing one or more suitable antimicrobial agents.  It is packaged in prefilled syringes or in vials containing not more than 30 mL of the water.  The container label must state the names and proportions of the antimicrobial agent or agents.

27.  The water is employed as a sterile vehicle in the preparation of small volumes of injectable preparations.  Theoretically, presence of the bacteriostatic agent gives the flexibility for multiple-dose vials.  USP labeling requirements demand that the label state “ Not for use in neonates ”.

28. To be continued ….