High concentrations of negative air ions (NAIs) and low concentrations of positive air ions (PAI), along with a low monopole coefficient (PAI/NAI), are likely to provide physiological and psychological benefits to the humans. A water body produces NAIs through the Lenard effect. This concept can be applied in designing garden waterscapes in residential buildings to provide fresh and healthy air for urban residents. In this study, we conducted several experiments to assess the effectiveness of different waterscape designs in producing air ions. The results revealed that increasing waterfall tiers, slopes, impact points, widths, and heights increased the NAI concentrations and reduced the values of monopole coefficients, thus providing health benefits to humans. In particular, increasing waterfall tiers and slopes increased the NAI concentrations most substantially. Moreover, we established a composite waterscape and determined that it produced fewer NAIs along with a less favorable monopole coefficient compared with the data observed at the experimentally adjusted tiers and slopes. Therefore, we suggest that simple waterscapes with multiple waterfall tiers or steep waterfall slopes should be favored over complex waterscapes. Such simple designs can help construct a garden that provides health benefits.