diff --git a/api.lua b/api.lua
index b11f5f3..264433b 100644
--- a/api.lua
+++ b/api.lua
@@ -21,7 +21,11 @@ local internal = dofile(modpath .. "/internal.lua")
 -- @param node_name string Name of the node, e.g. "default:water_source"
 -- @return number ID of the liquid
 function liquid_physics.get_liquid_id(node_name)
-    return internal.get_liquid_id(node_name)
+    local id = internal.get_liquid_id(node_name)
+    if id == 0 then
+        return nil
+    end
+    return id
 end
 
 -- Returns the liquid of the position specified or
@@ -30,7 +34,7 @@ end
 -- @return    table Table with liquid_id and liquid_level
 function liquid_physics.get_liquid_at(pos)
     local lpn = internal.new_lpn(core.hash_node_position(pos), pos)
-    if not lpn.liquid_id then
+    if not lpn.liquid_id or lpn.liquid_id == 0 then
         return nil
     end
     return { liquid_id = lpn.liquid_id, liquid_level = lpn.liquid_level }
@@ -43,7 +47,7 @@ end
 -- @param liquid_level number [0..8] Level of the liquid
 -- @return             bool   Success
 function liquid_physics.set_liquid_at(pos, liquid_id, liquid_level)
-    if liquid_level > 8 then
+    if liquid_level < 0 or liquid_level > 8 then
         return false
     end
     local lpn = internal.new_lpn(core.hash_node_position(pos), pos)