Make a surrounding structure, and start filling in the water with gravel or sand from the surface. Make complete rows: like this. Then dig underneath, put torches 1 row at a time and dig up until it falls: Like I'm about to do here. Just don't release a row without having another row behind it to hold the wall of water. Then you can collect the sand/gravel and make the next row, so you need a minimum of 2 rows at maximum width that you can reuse easily. This also uses no tools.