Governments have designated and operated water-friendly spaces in rivers in order to offer opportunities for refreshment and leisure to citizens. However, there are difficulties in providing convenience facilities for those spaces, mainly because of a conservative tradition related to the river space use permit. In this regard, this study present a novel method to estimate the adequate number of toilets and parking lots, as examples of convenience facilities, which citizens have often asked to provide. This study suggests two-steps approach: first, estimating statistically the rough number of convenience facilities from the key design variable, i.e., number of visitors; second, adjusting the number based on auxiliary design variables, i.e., areas of spaces and per capita visiting distance. Moreover it is found that mobile big data could be a good data source for building the statistical equation and investigating design variables for each water-friendly space. Finally, it describes a need for further studies and importance of managers’ and practitioners’ participation in improving the proposed method.