Synonyms

Aqua; hydrogen oxide.

Potable water Public supply suitable for drinking, the purity

of which is unlikely to be suitable for use in the manufacture of pharmaceuticals.

Purified water Vehicle and solvent for the manufacture of

drug products and pharmaceutical preparations; not suitable for use in the manufacture of parenteral products.

Chemical Name and CAS Registry Number

Water [7732-18-5]

Empirical Formula and Molecular Weight

H2O 18.02

Sterile water for inhalation Sterile water for injection

Sterile water for irrigation

Water for injections in bulk

Diluent for inhalation therapy products. Diluent for injections.

Diluent for internal irrigation therapy products.

Water for the bulk preparation of medicines for parenteral administration.

Structural Formula

H2O

Functional Category

Solvent.

Applications in Pharmaceutical Formulation or Technology

Water is the most widely used excipient in pharmaceutical production operations. Specific grades of water are used for particular applications in concentrations up to 100%; see Table

I. Purified water and water for injection are also used for cleaning operations during production of pharmaceutical products.

Description

The term ‘water’ is used to describe potable water that is freshly drawn direct from the public supply and is suitable for drinking. The chemical composition of potable water is variable and the nature and concentrations of the impurities in it depend upon the source from which it is drawn. Although potable water must be both palatable and safe to drink, for most pharmaceutical applications potable water is purified by distillation, ion exchange treatment, reverse osmosis, or some other suitable process to produce ‘purified water’. For certain applications, water with pharmacopeial specifications differing from those of purified water should be used, e.g. water for injection; see Sections 9 and 18.

Water is a clear, colorless, odorless, and tasteless liquid.



Pharmacopeial Specifications

See Table II.

Typical Properties

Boiling point: 1008C

Critical pressure: 22.1 MPa (218.3 atm) Critical temperature: 374.28C Dielectric constant: D25 = 78.54

Dipole moment:

1.76 in benzene at 258C;

1.86 in dioxane at 258C.

Ionization constant: 1.008 × 10—14 at 258C.

Latent heat of fusion: 6 kJ/mol (1.436 kcal/mol)

Latent heat of vaporization: 40.7 kJ/mol (9.717 kcal/mol)

Melting point: 08C

Refractive index: n20 = 1.3330

Solubility: miscible with most polar solvents.

Specific gravity: 0.9971 at 258C.

Specific heat (liquid): 4.184 J/g/8C (1.00 cal/g/8C) at 148C. Surface tension: 71.97 mN/m (71.97 dynes/cm) at 258C. Vapor pressure: 3.17 kPa (23.76 mmHg) at 258C. Viscosity (dynamic): 0.89 mPa s (0.89 cP) at 258C.