法華義疏 9.165

9.165

正言水隱地下，如佛性之不顯，故水譬佛性也。竺道生及《注法華經》云「此對小乘教求佛，故知去佛遠，就法華教求佛，故去佛近也」。

It is precisely because water is hidden underground, just as Buddha-nature is unmanifest; therefore water is a parable for Buddha-nature. Zhu Daosheng and the Commentary on the Lotus Sūtra say: "This is contrasted with seeking the Buddha in the Hīnayāna teachings, hence one knows one is far from the Buddha; seeking the Buddha in the Lotus teaching, hence one is near to the Buddha."