/* Check whether the third tile is an aqueduct head, or a water tile
	 * with one corner raised with or without a rail track, or a buoy. */
	if (!IsTileType(tile_cur, MP_WATER)) {
		if (IsTileType(tile_cur, MP_TUNNELBRIDGE)) {
			if (GetTunnelBridgeTransportType(tile_cur) != TRANSPORT_WATER) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
		} else if (IsTileType(tile_cur, MP_RAILWAY)) {
			if (GetRailGroundType(tile_cur != RAIL_GROUND_WATER)) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
		} else if (!IsBuoyTile(tile_cur)) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
	} else if (!IsTileFlat(tile_cur) && !IsSlopeWithOneCornerRaised(GetTileSlope(tile_cur))) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);