A little bit of web searching reveals that aluminum is a better choice for freshwater applications and zinc works better for salt water (marine use). Apparently in fresh water, a zinc anode can form a layer that will negate (no pun intended) the sacrificial effects.
Someone please correct me if I'm wrong but wouldn't it make sense the more pure the water the less corrosive effects anyway?? I think it's the dissolved mineral content (soluble salts) in the water that makes it act like an electrolyte creating a small voltage pressure. It's the small voltage pressure that cause the corrosion.
