When Hakone Gardens started in 1915, water wasn't a consideration. But after more than 100 years, climate change, and the current drought keeping a Japanese garden healthy is a challenge, especially the bamboo plants. The climate in Japan is moister that California. It is more like the Pacific Northwest. When I visited Hakone, they had just watered the gardens. This leaf looked particularly healthy after its bath.
One of the groundskeepers told me that rain distresses the gardeners because they see precious drops of water rolling away. Water, that if they could catch and retain, could be used to nourish the plants on dry days. I was told that a water reclamation system was too expensive to be practical.