To model the total amount of water \( w \) that Martina used, we can represent it as the product of the amount of water in each container and the number of containers.
Given that each of the 5 containers has 8.5 ounces of water, the equation can be set up as follows:
\[ w = 8.5 \times 5 \]
So, the completed equation is:
\[ w = 8.5 \times 5 \]