Water Point Mapping has been extensively used in Tanzania. An enhanced approach, including quality and seasonality of water points has been recently applied in Same District, Tanzania. This paper shows the results of extrapolating the influence of Water Quality and Seasonality in access to water in three central regions of Tanzania,: Dodoma, Tabora and Singida, covering a rural population of 4.5 million, in three statistical scenarios. Influence is assessed by type of water point. The most probable scenario shows that 56% of all rural population served by functional improved water points would be drinking unsafe water from improved water points. Conclusions highlight that the assumption that improved water points provide safe and sustainable water must be revised. More flexible policies towards service provision and revised indicators to track sector evolution should be adopted.