How to Make a Water Block in Minecraft

Set your game to creative mode. When you create a world it will say Game Mode: Survival. Click this and it will switch to Game Mode: Creative.

Find or create four slabs. You will find them in the Building Blocks section in the first section.

Make or obtain a water bucket. Water buckets are in Miscellaneous, the very last section of inventory and recipes.

Dig a one block deep "cross" shape in the ground. The cross should be 5 blocks. First dig one central block out, then on each of the edges of that block, mine one block in each direction.

Put a slab in the middle dugout block. This can be any kind of slab. Place slabs on the top and the inside of the outer mined out blocks as well. It should look like you've mined 2 blocks in the middle, and filled it with one, different block. The slabs don't need to match.

Place water on the middle, sunk-in slab.

Complete the water block. Point your crosshair on the water, and hit the mine button (right trigger) and the pick block button (go for right arrow) at the same time. A water block should appear in your inventory.