Frugal innovations are often associated with sustainable development. These connections, however, are based on anecdotal assumptions rather than empirical evidence. This article evaluates the sustainability of four frugal innovations from water and energy sectors. For the purposes of the evaluation, a set of indicators was developed. Indicators are drawn from sustainable development goals by the United Nations and they encompass central dimensions of sustainability: ecological, social and economic. In this article, frugal innovations are compared to solutions that are currently used in similar low-income contexts. Studied frugal innovations were found more sustainable in terms of energy production and water purification capacity than the existing solutions. In terms of social sustainability, larger differences between innovations were found. For example, business models of frugal energy solutions focus on capacity building and the inclusion of marginalized low-income people, whereas business models of water purification solutions focus on more traditional corporate social responsibility activities, such as marketing awareness campaigns and cooperation with non-governmental organizations. Three major sustainability challenges for frugal innovators were identified: (1) the proper integration of material efficiency into product or service systems; (2) the patient promotion of inclusive employment; and (3) the promotion of inclusive and sustainable local industrialization. The article concludes that despite indisputable similarities between frugality and sustainability, it is problematic to equate the two conceptually.