Previous research learned that the reproducibility of visual sewer inspection data is poor (Dirksen et al.). Further research by Arjan et al. showed that the applied coding system has a major influence on the reproducibility. The aim of this study was to give relevant suggestions to improve the quality by defining defects that are in the current standard defined ambiguously (i.e. can be understood in more than one way). For this, the database of sewer examination data of graduated sewer inspectors in the Netherlands was studied.