Instead of chlorine, a swimming pool in Judea was built using two types of plants to self cleanse – reeds and rushes. And it is precisely those two plants that Isaiah speaks about in chapter 37

Torrid earth shall become a pool; Parched land, fountains of water; The home of jackals, a pasture; The abode [of ostriches], reeds and rushes. (Isaiah 35:7)

Source: Israel in the News