To model the total amount of water, \( w \), that Martina used in her experiment, you can use the equation:
\[ w = 8.5 \text{ ounces} \times 5 \text{ containers} \]
So, the equation that models the total amount of water would be:
\[ w = 8.5 \times 5 \]
Calculating that gives:
\[ w = 42.5 \text{ ounces} \]
Thus, the total amount of water used by Martina is 42.5 ounces.