diff --git a/water_cmd.c b/water_cmd.c
--- a/water_cmd.c
+++ b/water_cmd.c
@@ -2,6 +2,7 @@
 #include "openttd.h"
 #include "table/sprites.h"
 #include "table/strings.h"
+#include "functions.h"
 #include "map.h"
 #include "tile.h"
 #include "vehicle.h"