Domestic water insecurity harms quality of life outcomes beyond health, for example in worry about water availability or anger at disrupted plans. However, these outcomes are excluded from cost-benefit analyses of water supply interventions, which typically measure and value only prevented disease and time savings. In this paper, I propose a means of quantifying the value of being water secure for an individual's quality of life, the water-adjusted person year (WAPY). One WAPY represents a year lived in complete water security. It is inspired by the quality-adjusted life year in health economics, which combines time with a health-related quality of life index. The WAPY combines time using water services with a water-related quality of life (WaterQoL) index, where 0 = completely water insecure and 1 = completely water secure. The index could be derived from an existing four-attribute Water Insecurity Experiences scale, which includes questions such as "how often did you worry that you would not have enough water for all of your needs?". Other questions concern drinking water, disrupted plans, and handwashing. Responses can be combined in a weighted index based on the relative importance of the four attributes to people. If someone has a WaterQoL index of 0.6, over a 10 year period they would have 6 WAPYs. If a water supply intervention raised WaterQoL to 0.8, they would gain 2 WAPYs over 10 years. The monetary value of WAPYs gained (e.g. in US$) could be estimated by willingness to pay and included in a cost-benefit analysis. Some interventions might result in greater WaterQoL gains than others, or longer-lasting services. Incorporating WAPYs in cost-benefit analyses, alongside prevented disease and time savings, could help identify interventions which provide better water services to more people within a given budget.