Hi Alex! 
Thank you for reaching out, I am happy to help answer this question. 

Based on the pictures, your witch hazel has sun scorch from the hot weather. Witch hazel is a partial sun to full shade tolerant plant. It can do well in full sun but with the heat we’ve had, it can scorch the leaves. The best way to help the plant is watering it more frequently, which you have been doing. The leaves might fall off but the plant should be ok if that happens. For reference,  here is a fact sheet about witch hazel that I pulled this info from: 

https://extension.umd.edu/resource/common-witchhazel/

If you see any other symptoms or the plant is looking worse, please reach out again. 
Have a great weekend! 

Chantal Rogers, CCE Master Gardener Volunteer