What is the velocity of tap water and what is the velocity of pressure washer? ?

Impossible questions to answer.  Each city, county, district, etc., has it own water system.  The velocity is going to be different in every one.  Plus it will be different for each person who has a pump and well water. There is no one velocity for all tap water.  And pressure washers come a large variety of different models, sizes, and powers.  There is no one velocity for all pressure washers.