how do you make concrete in minecraft?

fastest way i've found for a full stack: stand in shallow water, place the powder in front of you so it touches the water, mine it straight away, repeat. it converts instantly so you can just hold both buttons down and walk along.

sand, gravel and any dye gives you concrete powder - four sand, four gravel, one dye, eight powder out. i suspect that's already where you are. the powder isn't the block though: it has to be placed and then touched by water before it hardens, and after that only a pickaxe gets it back. mine it with anything else and it just vanishes.