Answer C. "Evidence that restrictions effectively save significant amounts of water."
Facts are always better to use when supporting a claim.
The interview might explain that people who water their lawn too frequently are more likely to harm rather than help. Except, this isn't a true fact because there is no causation between people watering their lawn too much and doing more harm.
A survey might show a popular vote, but the majority could possibly have voted for something based on opinions instead of facts.
This is a true fact because their is evidence of a causation between watering restrictions and saving water. By restricting the amount of water people can use for their lawns, water is being saved.
A claim isn't a fact that can be used for supportive details.