To model the total amount of water \( w \) Martina used, you can multiply the amount of water in each container by the number of containers she used. Since she has 5 containers, each containing 8.5 ounces of water, the equation would be:
\[ w = 8.5 , \text{ounces} \times 5 , \text{containers} \]
Therefore, the complete equation is:
\[ w = 8.5 \times 5 \]