Campaign-style environmental implementation (CEI) is widely exerted in environmental protection, while its benefits and costs are controversial. We take advantage of the Central Environmental Protection Inspection (CEPI) System— a latest and distinguished form of CEI launched by China in 2016, as a quasi-natural experiment to compare the benefits and costs of CEI based on water pollution effects estimates. Our results based on the annual panel data from 500 cities during 2009-2018 show that CEPI significantly reduced water pollution by an average of 11.2%. Further cost-benefit analysis based on the estimates of water pollution reduction shows that the potential health benefits of mortality and morbidity reduction resulting from CEPI are at least $279.5 billion, which is greater than the $192.2 billion economic losses it causes. The gap is further magnified after considering the potential biases. We also explore why CEPI is cost-effective and find that CEPI reduces water pollution and becomes cost-effective mainly through deterring local officials, punishing polluting enterprises, and increasing public participation in environmental governance.