Decentralized water treatment technologies could help in addressing global key water issues. Their successful implementation, however, depends on users' positive valuation and, depending on the technology, 'passive' use (rooted in acceptance), 'engaged' use (rooted in support) or 'active' use (rooted in behaviour change). Although users' valuation of a technology is contingent on its characteristics, positive valuation and use usually also require supporting promotion activities. Here we review the literature on psychological determinants of use as well as change techniques to promote use, and propose a user-focused theory of change to guide promotions. Our review highlights a lack of (conclusive) evidence on both psychological determinants and effective change techniques. We call on environmental and health psychologists to intensify their research on 'passive', 'engaged' and 'active' use of decentralized water treatment technologies and encourage engineers, practitioners and psychologists to intensify collaboration to ensure that technologies, implementation and promotions are optimally integrated.