This is the 2675th most frequent Japanese word.
洗っ
"洗っ" is the stem form of the verb "洗う," which means "to wash."
In this sentence, "洗っ" originates from the verb "洗う" (to wash) and is used in the present progressive form "洗っています" to describe a habitual action.
私は毎朝顔を洗っています。
I wash my face every morning.
Here, "洗っ" comes from "洗う," used in its past tense "洗った" to indicate a completed action.
彼は泥だらけの手を洗った。
He washed his mud-covered hands.
The verb "洗っ", conjugated here as "洗わ" followed by "なければなりません" (must), conveys an obligation to wash.