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 she used. Since she put 8.5 ounces of water into each of the 5 containers, the equation would be:
\[ w = 8.5 \times 5 \]
So, the completed equation is: \[ w = 8.5 \times 5 \]
To solve for \( w \):
\[ w = 42.5 \]
Therefore, the total amount of water she used is 42.5 ounces.