You have just enjoyed taking a shower when you notice the water is not draining. This really is not surprising with all the hair that continually is lost and washes down the drain. There could also be a buildup of all the soap scum. You could try some of the commercial products that the store offers if you do not mind breathing the fumes and toxic ingredients. The water has to be removed from the shower. Grab a bucket and a plastic cup and start bailing the water. As the bucket is filled you can just dumb it down the toilet. Get all the water that you can before stopping. Get a metal hanger and straighten it completely out. Insert it down the drain and try removing any debris that could be causing the clog. Continually move the hanger around then pull it back up so the hair and anything else can be thrown in the trash. Now go to the kitchen and get the vinegar and baking soda. You are going to pour these down the drain. As they mix together there will be lots of bubbling and foaming, so it is important to have something to cover the drain with. Pour about ? a cup of the baking soda down the drain slowly. Next pour about ? a cup of the vinegar down the drain then cover. This will need to sit in the pipes for about 30 minutes. Grab a pan and fill it with about a gallon of water. Turn the burner on and let the water come to a rolling boil. Carefully remove the pan from the stove and walk with it to the shower. Slowly pour the hot water down the shower drain for clearing. This is how to unblock a Blocked shower Clerkenwell.