The Huawei P20 Pro is waterproof, it's IP67 certified for water and dust. However, it's not as good as the Samsung Galaxy S9+ that carries a IP68 certification. IP67 means that it's dust tight the same as IP68, but the X7 means that it can only be submerged in water up to 1 meter, whether 7 rating means that you can submerge it up to 1.5 meters, both for up to 30 minutes in fresh water.
It's great to see that the phone is waterproof and I don't think the different between IP67 and IP68 would mean a lot to users. Nowadays, every flagship smartphone should be waterproof if it wants to compete against its peers.
Of course this doesn't mean that you should take it into the pool when you go to swim, it just helps to protect the phone against accidental water spill damage and allow you to use it in the rain without worrying about anything bad happening to your phone.