ISO 5815-2:2003规定了未稀释样品水生化需氧量的测定。本标准适用于所有生化需氧量大于或等于0.5 mg/l氧气（测定极限）且不超过6 mg/l氧气的水域。 获得的结果是生化和化学反应结合的产物。它们没有单一的、定义明确的化学过程所产生的严格而明确的特性。尽管如此，它们提供了一个指标，可以据此估计水质。 测试可能会受到各种物质存在的影响。对微生物有毒的物质，例如杀菌剂、有毒金属或游离氯，会抑制生化氧化。藻类或硝化微生物的存在会产生人为的高效果。 在这些情况下，可能需要修改方法。 附件A描述了替代的潜伏期。 附录B描述了通过添加种子材料、盐、通过添加烯丙基硫脲（ATU）抑制硝化、中和、均质和/或过滤来修改方法的程序。可能会发现，对接收水的水质进行具体评估时，这些修改是必要的。 附件C提供了精度数据。

ISO 5815-2:2003 specifies determination of the biochemical oxygen demand of waters of undiluted samples. It is applicable to all waters having biochemical oxygen demands greater than or equal to 0,5 mg/l of oxygen (the limit of determination) and not exceeding 6 mg/l of oxygen. The results obtained are the product of a combination of biochemical and chemical reactions. They do not have the rigorous and unambiguous character of those resulting from, for example, a single, well-defined, chemical process. Nevertheless, they provide an indication from which the quality of waters can be estimated. The test can be influenced by the presence of various substances. Those which are toxic to microorganisms, for example bactericides, toxic metals or free chlorine, inhibit biochemical oxidation. The presence of algae or nitrifying microorganisms can produce artificially high results. In these situations a modification of the method may be necessary. Annex A describes alternative incubation periods. Annex B describes procedures for modification of the method by addition of seeding material, salts, inhibition of nitrification by allylthiourea (ATU) addition, neutralization, homogenization and/or filtration. These modifications may be found necessary for specific evaluations of the water quality of receiving waters. Annex C provides precision data.