Use of Certified Reference Materials and Participation in Proficiency Testing by Water Testing Laboratories in Indonesia

Ensuring reliable water quality testing requires the use of Certified Reference Materials (CRMs) and participation in Proficiency Testing (PT). This study surveyed 244 accredited water testing laboratories in Indonesia, of which 28 laboratories (11.5%) responded. The results show that 85.7% of laboratories have implemented CRMs, although only a small proportion possess standard solution and matrix CRMs, and not all testing parameters are covered. CRM availability remains limited, with heavy reliance on international suppliers, while domestic production is underdeveloped compared to other ASEAN countries. Regarding PT, 22 laboratories reported participation, with ERA-Waters being the most frequently used provider; however, key parameters such as sulfide, barium, and pesticides are not yet included in existing PT schemes. These findings highlight the urgent need to strengthen domestic CRM production, expand PT coverage, and reinforce regulatory support to enhance measurement traceability and align Indonesia's water testing practices with international standards.