Well, you can make 2 maps, with water and without water, and teleport. This would be the easy way xDD
But you can change a tile with a call script:
$game_map.data[x,y,a] = b+384
a is the layer: 0 to 2
b is the number of the tile on the tileset
Example:
$game_map.data[10,9,0] = 2+384
I did a script that replaces all the tiles of a number by another like in 2k.
#==============================================================================
# Replace Tile AddOn
# ---------------------------
=begin
With this script you can replace tiles of a map like in RPG maker 2k.
To call this on map, insert the next code on a Script command:
$game_map.replace_tile(tile1,tile2,layer,autotile)
tile1 => integer, initial tile of the tileset
tile2 => integer, final tile of the tileset
(layer) => integer, which layer will be altered (0 to 3) or all layers (-1)
it equals -1 by default
(autotile) => if true, the change will be on autotiles
it's set false by default
=end
#==============================================================================
class Game_Map
def replace_tile(a,b,layer=-1,autotile=false)
@layer = layer
if autotile == false
for i in 0..width
for j in 0..height
if @layer == -1
for l in 0..2
data[i,j,l] = b+384 if data[i,j,l] == a+384
end
else
l = @layer
data[i,j,l] = b+384 if data[i,j,l] == a+384
end
end
end
else
a0 = a*48 ; a1 = (a+1)*48
b0 = b*48 ; b1 = (b+1)*48
a_array = []
b_array = []
for i in a0...a1
a_array.push(i)
end
for i in b0...b1
b_array.push(i)
end
for i in 0..width
for j in 0..height
if @layer == -1
for l in 0..2
for k in 0..a_array.size
data[i,j,l] = b_array[k] if data[i,j,l] == a_array[k]
end
end
else
l = @layer
for k in 0..a_array.size
if data[i,j,l] == a_array[k]
data[i,j,l] = b_array[k]
end
end
end
end
end
end
end
end
How to use:
$game_map.replace_tile(tile1,tile2,layer,autotile)
autotile --> true / false