To represent the total cost for a customer who purchases \( w \) car washes, you can use the following expression:
\[ \text{Total Cost} = 5 + 14w \]
In this expression:
- \( 5 \) represents the one-time fee for supplies.
- \( 14w \) represents the total cost for the \( w \) car washes, where \( 14 \) is the charge per car wash and \( w \) is the number of car washes purchased.