diff --git a/src/water_map.h b/src/water_map.h
--- a/src/water_map.h
+++ b/src/water_map.h
@@ -16,27 +16,31 @@
 #include "depot_type.h"
 #include "tile_map.h"
 
+/** Available water tile types. */
 enum WaterTileType {
-	WATER_TILE_CLEAR,
-	WATER_TILE_COAST,
-	WATER_TILE_LOCK,
-	WATER_TILE_DEPOT,
+	WATER_TILE_CLEAR, // Plain water.
+	WATER_TILE_COAST, // Coast.
+	WATER_TILE_LOCK,  // Water lock.
+	WATER_TILE_DEPOT, // Water Depot.
 };
 
+/** classes of water (for #WATER_TILE_CLEAR water tile type). */
 enum WaterClass {
-	WATER_CLASS_SEA,
-	WATER_CLASS_CANAL,
-	WATER_CLASS_RIVER,
-	WATER_CLASS_INVALID, ///< Used for industry tiles on land (also for oilrig if newgrf says so)
+	WATER_CLASS_SEA,     ///< Sea.
+	WATER_CLASS_CANAL,   ///< Canal.
+	WATER_CLASS_RIVER,   ///< River.
+	WATER_CLASS_INVALID, ///< Used for industry tiles on land (also for oilrig if newgrf says so).
 };
 template <> struct EnumPropsT<WaterClass> : MakeEnumPropsT<WaterClass, byte, WATER_CLASS_SEA, WATER_CLASS_INVALID, WATER_CLASS_INVALID, 2> {};
 
+/** Sections of the water depot. */
 enum DepotPart {
 	DEPOT_NORTH = 0x80,
 	DEPOT_SOUTH = 0x81,
 	DEPOT_END   = 0x84,
 };
 
+/** Sections of the water lock. */
 enum LockPart {
 	LOCK_MIDDLE = 0x10,
 	LOCK_LOWER  = 0x14,
@@ -44,6 +48,10 @@ enum LockPart {
 	LOCK_END    = 0x1C
 };
 
+/** Get the water tile type at a tile.
+ * @param t Water tile to query.
+ * @return Water tile type at the tile.
+ */
 static inline WaterTileType GetWaterTileType(TileIndex t)
 {
 	assert(IsTileType(t, MP_WATER));
@@ -56,12 +64,20 @@ static inline WaterTileType GetWaterTile
 	return WATER_TILE_DEPOT;
 }
 
+/** Get the water class at a tile.
+ * @param t Water tile to query.
+ * @return Water class at the tile.
+ */
 static inline WaterClass GetWaterClass(TileIndex t)
 {
 	assert(IsTileType(t, MP_WATER) || IsTileType(t, MP_STATION) || IsTileType(t, MP_INDUSTRY));
 	return (WaterClass)(IsTileType(t, MP_INDUSTRY) ? GB(_m[t].m1, 5, 2) : GB(_m[t].m3, 0, 2));
 }
 
+/** Set the water class at a tile.
+ * @param t  Water tile to change.
+ * @param wc New water class.
+ */
 static inline void SetWaterClass(TileIndex t, WaterClass wc)
 {
 	assert(IsTileType(t, MP_WATER) || IsTileType(t, MP_STATION) || IsTileType(t, MP_INDUSTRY));
@@ -72,84 +88,147 @@ static inline void SetWaterClass(TileInd
 	}
 }
 
-/** IsWater return true if any type of clear water like ocean, river, canal */
+/** Is it a plain water tile?
+ * @param t Water tile to query.
+ * @return \c true if any type of clear water like ocean, river, or canal.
+ */
 static inline bool IsWater(TileIndex t)
 {
 	return GetWaterTileType(t) == WATER_TILE_CLEAR;
 }
 
+/** Is it a sea water tile?
+ * @param t Water tile to query.
+ * @return \c true if it is a sea water tile.
+ */
 static inline bool IsSea(TileIndex t)
 {
 	return IsWater(t) && GetWaterClass(t) == WATER_CLASS_SEA;
 }
 
+/** Is it a canal tile?
+ * @param t Water tile to query.
+ * @return \c true if it is a canal tile.
+ */
 static inline bool IsCanal(TileIndex t)
 {
 	return IsWater(t) && GetWaterClass(t) == WATER_CLASS_CANAL;
 }
 
+/** Is it a river water tile?
+ * @param t Water tile to query.
+ * @return \c true if it is a river water tile.
+ */
 static inline bool IsRiver(TileIndex t)
 {
 	return IsWater(t) && GetWaterClass(t) == WATER_CLASS_RIVER;
 }
 
+/** Is it a water tile with plain water?
+ * @param t Tile to query.
+ * @return \c true if it is a plain water tile.
+ */
 static inline bool IsWaterTile(TileIndex t)
 {
 	return IsTileType(t, MP_WATER) && IsWater(t);
 }
 
+/** Is it a coast tile?
+ * @param t Water tile to query.
+ * @return \c true if it is a sea water tile.
+ */
 static inline bool IsCoast(TileIndex t)
 {
 	return GetWaterTileType(t) == WATER_TILE_COAST;
 }
 
+/** Get the other tile of the ship depot.
+ * @param t Tile to query, containing one section of a ship depot.
+ * @return Tile containing the other section of the depot.
+ */
 static inline TileIndex GetOtherShipDepotTile(TileIndex t)
 {
 	return t + (HasBit(_m[t].m5, 0) ? -1 : 1) * (HasBit(_m[t].m5, 1) ? TileDiffXY(0, 1) : TileDiffXY(1, 0));
 }
 
+/** Is it a water tile with a ship depot on it?
+ * @param t Water tile to query.
+ * @return \c true if it is a ship depot tile.
+ */
 static inline bool IsShipDepot(TileIndex t)
 {
 	return IsInsideMM(_m[t].m5, DEPOT_NORTH, DEPOT_END);
 }
 
+/** Is it a ship depot tile?
+ * @param t Tile to query.
+ * @return \c true if it is a ship depot tile.
+ */
 static inline bool IsShipDepotTile(TileIndex t)
 {
 	return IsTileType(t, MP_WATER) && IsShipDepot(t);
 }
 
+/** Get the axis of the ship depot.
+ * @param t Water tile to query.
+ * @return Axis of the depot.
+ */
 static inline Axis GetShipDepotAxis(TileIndex t)
 {
 	return (Axis)GB(_m[t].m5, 1, 1);
 }
 
+/** Get the direction of the ship depot.
+ * @param t Water tile to query.
+ * @return Direction of the depot.
+ */
 static inline DiagDirection GetShipDepotDirection(TileIndex t)
 {
 	return XYNSToDiagDir(GetShipDepotAxis(t), GB(_m[t].m5, 0, 1));
 }
 
+/** Is it a water lock tile?
+ * @param t Water tile to query.
+ * @return \c true if it is a water lock tile.
+ */
 static inline bool IsLock(TileIndex t)
 {
 	return IsInsideMM(_m[t].m5, LOCK_MIDDLE, LOCK_END);
 }
 
+/** Get the direction of the water lock.
+ * @param t Water tile to query.
+ * @return Direction of the lock.
+ */
 static inline DiagDirection GetLockDirection(TileIndex t)
 {
 	return (DiagDirection)GB(_m[t].m5, 0, 2);
 }
 
+/** Get a section of a depot or a lock.
+ * @param t Water tile to query.
+ * @return The section.
+ */
 static inline byte GetSection(TileIndex t)
 {
 	assert(GetWaterTileType(t) == WATER_TILE_LOCK || GetWaterTileType(t) == WATER_TILE_DEPOT);
 	return GB(_m[t].m5, 0, 4);
 }
 
+/** Get the random bits of the water tile.
+ * @param t Water tile to query.
+ * @return Random bits of the tile.
+ */
 static inline byte GetWaterTileRandomBits(TileIndex t)
 {
 	return _m[t].m4;
 }
 
 
+/**
+ * Helper function to make a coast tile.
+ * @param t The tile to change into water
+ */
 static inline void MakeShore(TileIndex t)
 {
 	SetTileType(t, MP_WATER);
@@ -212,6 +291,15 @@ static inline void MakeCanal(TileIndex t
 	MakeWater(t, o, WATER_CLASS_CANAL, random_bits);
 }
 
+/**
+ * Make a ship depot section.
+ * @param t    Tile to place the ship depot section.
+ * @param o    Owner of the depot.
+ * @param did  Depot ID.
+ * @param base Depot base (either #DEPOT_NORTH or #DEPOT_SOUTH).
+ * @param a    Axis of the depot.
+ * @param original_water_class Original water class.
+ */
 static inline void MakeShipDepot(TileIndex t, Owner o, DepotID did, DepotPart base, Axis a, WaterClass original_water_class)
 {
 	SetTileType(t, MP_WATER);
@@ -224,6 +312,13 @@ static inline void MakeShipDepot(TileInd
 	_me[t].m7 = 0;
 }
 
+/** Make a lock section.
+ * @param t Tile to place the water lock section.
+ * @param o Owner of the lock.
+ * @param section Section to place.
+ * @param original_water_class Original water class.
+ * @see MakeLock
+ */
 static inline void MakeLockTile(TileIndex t, Owner o, byte section, WaterClass original_water_class)
 {
 	SetTileType(t, MP_WATER);
@@ -236,6 +331,14 @@ static inline void MakeLockTile(TileInde
 	_me[t].m7 = 0;
 }
 
+/**
+ * Make a water lock.
+ * @param t Tile to place the water lock section.
+ * @param o Owner of the lock.
+ * @param d Direction of the water lock.
+ * @param wc_lower Original water class of the lower part.
+ * @param wc_upper Original water class of the upper part.
+ */
 static inline void MakeLock(TileIndex t, Owner o, DiagDirection d, WaterClass wc_lower, WaterClass wc_upper)
 {
 	TileIndexDiff delta = TileOffsByDiagDir(d);