use loud_walking:water_poison (via alias though)

deco.lua

@@ -114,6 +114,7 @@ newnode.tiles = {"underworlds_black_sand.png"}
 newnode.groups['falling_node'] = 0
 minetest.register_node("underworlds:black_sand", newnode)
 
+--[[
 newnode = underworlds_mod.clone_node("default:water_source")
 newnode.description = "Poisonous Water"
 newnode.groups.poison = 3
@@ -121,8 +122,8 @@ newnode.light_source = 6
 newnode.liquid_alternative_flowing = "underworlds:water_poison_flowing"
 newnode.liquid_alternative_source = "underworlds:water_poison_source"
 newnode.post_effect_color = {a = 103, r = 108, g = 128, b = 64}
-newnode.special_tiles[1].name = "underworlds_water_poison_source_animated.png"
-newnode.tiles[1].name = "underworlds_water_poison_source_animated.png"
+newnode.special_tiles = "underworlds_water_poison_source_animated.png"
+newnode.tiles = "underworlds_water_poison_source_animated.png"
 minetest.register_node("underworlds:water_poison_source", newnode)
 
 newnode = underworlds_mod.clone_node("default:water_flowing")
@@ -132,9 +133,12 @@ newnode.light_source = 6
 newnode.liquid_alternative_flowing = "underworlds:water_poison_flowing"
 newnode.liquid_alternative_source = "underworlds:water_poison_source"
 newnode.post_effect_color = {a = 103, r = 108, g = 128, b = 64}
-newnode.special_tiles[1].name = "underworlds_water_poison_flowing_animated.png"
-newnode.tiles[1] = "underworlds_water_poison.png"
+newnode.special_tiles = "underworlds_water_poison_flowing_animated.png"
+newnode.tiles = "underworlds_water_poison.png"
 minetest.register_node("underworlds:water_poison_flowing", newnode)
+]]
+minetest.register_alias("underworlds:water_poison_source", "loud_walking:water_poison_source")
+minetest.register_alias("underworlds:water_poison_flowing", "loud_walking:water_poison_flowing")
 
 -- ice, thin -- transparent
 minetest.register_node("underworlds:thin_ice", {