To model the total amount of water \( w \) that Martina used, you can multiply the amount of water in each container by the number of containers. Since she put 8.5 ounces of water into each of the 5 containers, the equation would be:
\[ w = 8.5 \times 5 \]
So, you can complete the equation as:
\[ w = 8.5 \times 5 \]