Step 1: The problem states that the bucket capacities are proportional to their ages. Since Tina is the eldest, her bucket is the largest, and since Bina is the youngest, her bucket is the smallest.
Step 2: Assume the ages of Tina, Mina, Gina, Lina, and Bina are \(5, 4, 3, 2, 1\) respectively (or in descending order with any proportional ratio). Then, their bucket capacities are also in the ratio \(5:4:3:2:1\).
Step 3: Suppose the equal amount of water lost by each sister is \(x\) liters. Then the fraction of water lost by each is:
\[
\text{Fraction lost} = \frac{x}{\text{bucket capacity}}.
\]
Step 4: For Tina, fraction lost \(= \frac{x}{5}\). For Mina \(= \frac{x}{4}\). For Gina \(= \frac{x}{3}\). For Lina \(= \frac{x}{2}\). For Bina \(= \frac{x}{1} = x\).
Step 5: Clearly, as the denominator decreases, the fraction lost increases. Hence, Bina (youngest, with the smallest bucket) loses the maximum water as a % of her bucket capacity.
\[
\boxed{\text{Bina loses the maximum percentage of water.}}
\]