While the public considers municipal water to be “pure”, the pharmaceutical market considers municipal water (feedwater) just the starting point in producing pure water. Water is the most widely used excipient in pharmaceutical manufacturing, and pharmaceutical water is a multi-functional resource, crossing all disciplines in the pharmaceutical industry. Water is used as a raw material, solvent, ingredient, reagent, and cleaning agent, and is produced in a variety of “pure” forms.
Purified Water (PW), Highly Purified Water (HPW), and Water for Injection (WFI) used in pharmaceutical processes are produced on site from the local potablewater, which has been produced by the treatment of the feedwater.
Today’s pharmaceutical companies have invested considerable capital in state-of-the-art instrumentation, purification equipment, storage and distribution loops,and importantly in the calibration and certification of their water systems. By understanding water, its sources and impurities, and the capabilities and limitations of purification methods, a water system can be designed to meet not only pharmaceutical companies’ requirements but to meet global pharmacopeia regulations.
Source water requirements
“It is prepared from water complying with the U.S. Environmental Protection Agency National Primary Drinking Water regulations or with the drinking water regulations of the European Union, Japan, or with the World Health Organization’s Guidelines forDrinking Water Quality.” USP 35
The feedwater source for a municipality can be from a surface water or a ground water supply. The impurities vary in each source and some of the primary differences are shown below:
Because the quality and characteristics of the feedwater supply have an important bearing on the purification, the pharmacopeias define the source water for the production of PW, HPW, and WFI. The pharmaceutical facility should communicate regularly with their water provider and request an annual water test report for the feedwater. To further the understanding of the feedwater and what technologies are required to purify it, below are the categories of contaminants found in a water supply.
Contaminants in feedwater
The impurities found in water can be categorized into six major classes: dissolved ionized solids, dissolved ionized gases, dissolved non-ionized solids (organics), particulate matter, bacteria/algae, and pyrogens. Feedwater varies significantly in purity both from one geographical region to another, and from season to season.
Total dissolved solids (TDS)
A measure of the total of organic and inorganic salts dissolved in water, obtained by drying residue at 180°C. The sum of all ions in a solution is often
approximated by means of electrical conductivity or resistivity measurements. TDS measurements are commonly used to assess reverse osmosis unit
Total ionized solids and gases
Concentration of dissolved ions in solution, expressed in concentration units of NaCI (sodium chloride). This determines the operating life of ion exchange resins used in water purification, and is calculated from measurements of specific resistance. Gases (carbon dioxide and oxygen) affect the water quality and system performance.
Total solids in water include both dissolved and suspended solids. The quantity of total solids is determined by weighing a sample of the feedwater before and after evaporation.
Bacteria, viruses, and pyrogens (endotoxins).
Sand, dirt, and decay material.
Organic matter is a broad category that includes both natural and man-made molecules containing carbon and hydrogen. All living matter in water is made up of organic molecules. The most common are by-products of vegetative decay such as tannins, lignins, and humic acid. By knowing the variety of contaminants in the water and the removal capabilities of the different available purification processes, a system can be designed that will produce the water quality required for a pharmaceutical facility. There are a range of purification technologies and we have provided below a brief description of the major purification technologies.
Major water purification technologies
The chart shown below is a summary of the removal capabilities of different purification technologies versus the contaminants commonly found in water.
PW, HPW, and WFI for pharmaceutical use are produced via a combination of different purification technologies. As with the source water, each pharmacopeia defines the methods of production, but for PW and HPW the technologies utilized is the decision of the system designer, with the only requirement being that the water meets the pharmacopeia regulations for quality. For WFI, to meet the pharmacopeia requirements (all pharmacopeias except Japan), the final purification process must be distillation.
Purifying the feedwater for use in the pharmaceutical industry requires a series of steps. The objective is to remove the impurities in the feedwater while minimizing additional contamination from the components of the purification system, the storage tanks, the distribution system, and from possible biofilm growth. Selection of the correct purification technologies and the instrumentation to monitor the system are critical to success.
Reverse osmosis is best understood when related to osmosis itself. In one of the experiments performed by everyone in first year chemistry, a semi-permeable membrane (a membrane that is permeable to water but not to salt) is used to separate two solutions; a saline solution and pure water. The pure water will flow through the membrane to dilute the saline solution. This is osmosis. When pressure is applied to the sa-line solution, the natural process of osmosis can be overcome and even reversed. With sufficient pressure, pure water can be forced out of the saline solution through the membrane and into the pure water side of the vessel. This is reverse osmosis.