Demand for safe water, as well as access to adequate and affordable products for drinking water treatment, is key for household water treatment (HWT) in low-income countries. Critical barriers, particularly in rural areas, are the lack of adequate marketing and sales models and the challenge of setting up distribution channels that reach low-income customers, leading to the unavailability of HWT products. Trials with four different social marketing and sales models, involving local entrepreneurs, staff of a non-governmental organization (NGO), community health workers and members of community-based organizations, were conducted in Kenya and Bolivia to test which marketing and sales strategies, as well as which behavioural determinants, influence product purchase and water treatment practices in different local contexts. Selling filters through the water utility, a community-based enterprise, was a promising retail model in Kenya and in Bolivia. Most successful were sales done by a women's group in Bolivia. We found that community education activities, independent of the stakeholder carrying out the activity, are an important element to create demand for water treatment products. Other factors influencing product purchase and practice are very context specific and include: the turbidity of water, risk perception, socio-economic status, social norms and emotional attributes.