When you want to dismantle the water tap, you must not use wrong tool or not really suitable for the job. In this case, do not use pipe wrench to grip and open the tap.

If you use pipe wrench, it is more difficult and you will fill the wrench is not gripping. Then you will realize that the tap slot was broken.

The correct tool is the spanner. The spanner come with various of size. So, to be easy you just need to buy one unit of adjustable spanner. Then, you can apply it with anything.

It very easy and it will not damage the tap slot. Actually, the slot is for specifically for spanner application.