Laboratory water purity is governed by internationally recognised standards that define the specifications water must meet for different analytical and industrial applications. The two most widely referenced standards are EN ISO 3696, published by the International Organization for Standardization, and ASTM D1193, maintained by ASTM International (formerly the American Society for Testing and Materials). While both standards serve the same fundamental purpose — classifying water by purity level — they differ in their grading structures, parameter thresholds, and geographic adoption.
EN ISO 3696 is the prevailing standard across Europe and is widely adopted by laboratories operating under European regulatory frameworks. It is commonly referenced in European Pharmacopoeia methods, CE-marked device manufacturing, and EU-regulated analytical workflows. The standard is also recognised in many countries that align their laboratory practices with ISO protocols.
ASTM D1193, by contrast, is the dominant standard in North America and has broad global adoption, particularly in industries influenced by US regulatory agencies such as the FDA and EPA. It is extensively referenced in United States Pharmacopeia (USP) methods, US federal testing protocols, and by multinational organisations that follow American analytical standards. Many laboratories outside North America also reference ASTM D1193 due to its detailed classification system and widespread use in published methods.
EN ISO 3696 classifies water into three grades:
ASTM D1193 provides a more granular classification with four types:
Both standards measure similar water quality parameters but set different thresholds:
The choice of standard often depends on the regulatory environment in which a laboratory operates. European pharmaceutical companies typically reference EN ISO 3696 alongside European Pharmacopoeia monographs, while their US counterparts follow ASTM D1193 in conjunction with USP specifications. Environmental testing laboratories in EU member states generally work to EN ISO standards, whereas those performing EPA methods use ASTM-classified water.
In practice, many international laboratories and contract research organisations must comply with both standards, depending on the client, method, or regulatory submission involved. Understanding the equivalences and differences between the two frameworks is therefore essential for maintaining compliance across multiple jurisdictions.
Waternation Scientific manufactures high-purity waters that meet or exceed the requirements of both EN ISO 3696 and ASTM D1193. Our product range includes waters classified to ASTM Type I through Type IV, as well as EN ISO 3696-compliant grades, enabling laboratories to source from a single trusted supplier regardless of which standard their methods require.
Every batch is manufactured under controlled cleanroom conditions with full traceability, and Certificates of Analysis are provided as standard, documenting compliance against the relevant specification. Our technical team can advise on cross-referencing between standards to ensure your water supply meets all applicable requirements.
EN ISO 3696 and ASTM D1193 are complementary standards that serve different regulatory and geographic markets. Understanding their differences — particularly in resistivity thresholds, TOC specifications, and silica limits — is essential for laboratories that operate internationally or must comply with methods referencing either framework. By sourcing from a manufacturer that meets both standards, laboratories can simplify their procurement while maintaining full compliance.
View our complete range of standards-compliant waters on our products page, or contact us for advice on selecting the right specification for your application.