Step 1: Wood Door
This is my first instructable so give me a chance. Get some wood and make a wooden door.It also works with trapdoors and fence gates if you put it on the floor.
Step 2: Creating the House
Find a spot underwater where there's no gravity effected blocks and dig 3 blocks down.
Step 3: Forming the House
Dig four blocks forward. Two each level then go there and place the door at the front closest to the source of the water. There should now be no water in the start of the house.
Step 4: Customising
Now can customise and you are done