Have you successfully exported a map from Tile Studio? If not I can help. If you have then you can do the following calculation:
PlayerTileX = ( ( PlayerPosX - ( PlayerPosX % TileSizeX ) ) / TileSizeX ) - 1
PlayerTileY = ( ( PlayerPosY - ( PlayerPosY % TileSizeY ) ) / TileSizeY ) - 1
where PlayerPos is the position of the player and TileSize is the size in pixels of one tile. That will give you the tile coordinates of the tile the player is on. Then you can access your tile array with PlayerTileX and PlayerTileY and check what image the tile is. If it's water then the player can't walk on it, otherwise he can.
