RunningCount of unique values

I have following columns in a query

Email

Week

I want unique users with "Email" every week as a running count. If on Week 1, 10 unique users uses the system, in Week 2, 13 unique users uses the system and 7 users are common it should show 6 new users (new users of Week2) + 10 (unique users of Week1) i.e. 16. In Week3, total 15 unique users out of which only 3 are new users

Week       UniqueUsers      Adoption

Week1       10                         10

Week2       13                         10+6   

Week3       15                         10+6+3