Sterility of Water for Injection (WFI)

Pharmaceutical and biopharmaceutical industries require high-quality water appropriate for the numerous clinical and research applications where microbial and chemical contaminants are a hazard. For these industries, water is often used to prepare cell culture media and buffers for research and development of therapeutics and to formulate the final drug products.

Pharmacopeia standards dictate the required water purity based on intended use. United States Pharmacopeia (USP) “purified water” and USP “water for injection” (WFI) must each meet specific standards, with higher standards for WFI than purified water.

This article focuses on water for injection: what it is, how it is used, and the standards it must meet. The article concludes with an overview of water products available from Teknova, highlighting the quality control processes and manufacturing standards involved in their production.

Water for Injection

WFI is a grade of water that meets purity standards required for the manufacturing of injectable drugs. However, WFI-grade water is essential at various stages of research and development in the pharmaceutical and biopharmaceutical industries. There are numerous applications of WFI throughout the preclinical and clinical stages of drug development. It can serve as highly pure water to reconstitute media, reagents, and buffers for cell culture and be used for resuspension and buffer exchange at the end of drug manufacture for final product formulation.

In the US and many other countries, the standards for WFI are dictated by the USP that specifies maximum levels of conductivity, total organic carbon (TOC), bacteria, and endotoxins (Table 1).

Table 1. United States Pharmacopeia (USP) Standards for Water.

Properties USP Water for Injection & USP Highly Purified Water* USP Purified Water
Conductivity (µS/cm at 25°C) <1.3 <1.3
Total Organic Carbon (TOC) (ppb or µg/L) <500 <500
Bacteria <10 CFU/100 mL <100 CFU/mL
Endotoxin (EU/mL) <0.25 Not applicable

* Standard used for water system by Teknova.

† EU = endotoxin units

Purity standards for water are also set by other agencies, one of which is the American Society for Testing and Materials (ASTM). ASTM outlines standards for laboratory reagent water (Table 2) from the highest quality, Type I (ultrapure), to the lowest quality, Type IV (semi-pure). The purity requirements for ASTM Type I—in comparison to USP—are higher for certain parameters (e.g., conductivity, TOC) and include additional specifications (e.g., resistivity, sodium, chloride, silica).

ASTM also stipulates microbiological specifications (e.g., bacteria, endotoxin): Type A water has the highest sterility, Type B is equivalent to USP WFI, and Type C only specifies a standard for bacteria levels and no threshold for endotoxin levels (Table 2).

Table 2. ASTM Standards for Laboratory Reagent Water.

Measurement (unit) Type I* Type II Type III Type IV
Conductivity (µS/cm) 0.056 1.0 4.0 5.0
Resistivity (MΩ-cm) 18 1.0 0.25 0.2
pH Not applicable Not applicable Not applicable 5–8
Total Organic Carbon (TOC) (ppb or µg/L) 50 50 200 No limit
Sodium (ppb or µg/L) 1 5 10 50
Chloride (ppb or µg/L) 1 5 10 50
Silica (ppb or µg/L) 3 3 500 No limit
Measurement (unit) Type A Type B Type C
Maximum heterotrophic bacteria count 10/1000 mL 10/100 mL 100/10 mL
Endotoxin (EU/mL) 0.03 0.25 Not applicable

* Standard used for water system by Teknova.

† pH measurements are not taken because these grades of water do not contain constituents at levels that would significantly alter the pH.

‡ EU = endotoxin units

Water at Teknova

Water used and supplied by Teknova undergoes two stages of manufacturing and quality control: the water system level (Stage 1) and at the water product level (Stage 2).

Stage 1: Water System

In Stage 1 of water manufacturing and quality control, the system level, water is continuously monitored at the source for resistivity and conductivity. Water samples at every point of use are tested weekly for endotoxin, bacteria, and TOC levels. Sodium, chloride, and silica levels are assessed monthly. These tests ensure the water system is continuously monitored for adherence to the USP standards for “USP WFI” (Table 1, gray shading) and the ASTM Standards for “ASTM Type I” (Table 2, gray shading). Water from this high-quality system is used for all Teknova products that are manufactured or formulated with water.

Stage 2: Water Products

Stage 2 of water manufacturing and quality control occurs at the product level, where each finished water product that Teknova sells undergoes its own quality control testing at bottling.

These may include tests for RNase, DNase, protease, bacterial DNA (PCR), and USP Sterility (USP ), as well as additional endotoxin testing. Teknova offers four grades of water that meet different research and development needs:

  • Cell Culture Grade Water: This type of water is suitable for cell and tissue culture because it has been tested for endotoxins.
  • Molecular Biology Grade PCR Certified Water: This water is appropriate for PCR applications as it has been DNase-, RNase-, and protease-tested, as well as PCR-verified for the absence of bacteria.
  • DEPC-Treated Water: This is water treated with diethyl pyrocarbonate (diethyl dicarbonate) to deactivate RNases. DEPC-Treated Water is suitable for working with RNA.
  • Reagent Grade Water: This water serves numerous applications (buffers, solutions, and microbiological media) that do not require additional quality control testing at bottling.

Additionally, some water products are documented as being manufactured under good manufacturing practices (GMP) for clinical applications; these products undergo additional testing, which is customer-defined and can include specific endotoxin levels, tighter specifications, and different sterility testing options (USP ). Contact us for more information about GMP reagents.

Manufacturing Standards for Water at Teknova

At Teknova, we have implemented many safeguards in our manufacturing processes to ensure that all water meets USP and ASTM Type I standards.

Microbial growth is a significant issue in the production of water. Teknova prevents microbial growth by using UV treatment, sterile filtration with a 0.1 µm filter, highly polished stainless steel, and a continuously circulating, easy-to-clean system.

Chemical contaminants, including organic, suspended, and colloidal contaminants, are controlled using deionization (using ion exchange resins), charged carbon adsorption resins, reverse osmosis, and UV treatment. For products that require a higher level of purity, glass distillation is performed in addition to the other purification methods.