To find the mass of the water in the mixture, we can use the following equation that relates the total mass of the mixture to the masses of its components:
\[ \text{Total Mass} = \text{Mass of Water} + \text{Mass of Salt} + \text{Mass of Iodine} \]
We are given the following information:
- Total mass of the mixture = 225 grams
- Mass of salt = 5.0 grams
- Mass of iodine = 15.0 grams
Now we can substitute the known values into the equation:
\[ 225 \text{ g} = \text{Mass of Water} + 5.0 \text{ g} + 15.0 \text{ g} \]
Now combine the masses of salt and iodine:
\[ 225 \text{ g} = \text{Mass of Water} + 20.0 \text{ g} \]
To isolate the mass of the water, we subtract 20.0 grams from both sides:
\[ \text{Mass of Water} = 225 \text{ g} - 20.0 \text{ g} = 205 \text{ g} \]
Thus, the mass of the water is:
\[ \boxed{205 \text{ grams}} \]