6x Sand + 6x Charcoal + 4x Gravel (used as natural filters).
Based on the Card Survival: Tropical Island base-building and survival mechanics, " Feature Name: The Hydro-Purification Hub Card.Survival.Tropical.Island.Build.10208160.zip
Large specialized funnels automatically collect rainwater, filling the internal 100L reservoir. 6x Sand + 6x Charcoal + 4x Gravel (used as natural filters)