The regulation of Swedish municipal accounting has gone through fundamental changes over recent decades. On 1 January 1998, municipal accounting became regulated by law, after having been merely voluntarily regulated in the past. Using the lens of agency theory as well as institutional theory, this paper explores how legislation and chosen form of association influence the harmonization of accounting and the application of generally accepted accounting principles in the Swedish water and sewage sector. Through comparisons of survey data from the year before and five years after the legislation, the study analyzes whether the legislation has affected the level of harmonization. Even though municipal accounting now is regulated by law, the requirements for aspects such as auditing are still much lower for municipals than for companies; the requirements for accountability are much lower for municipal agents than for companies. The study also analyzes whether there is any relationship between form of association and level of harmonization. The results do not indicate that the legislation had any effect on harmonization; neither do the results show any significant relationship between form of association and level of harmonization.