What do you mean by water equivalent of iron is greater than copper?

It means that when water has the thermal capacity equal to iron, that thermal capacity is greater than that of copper.

Explanation:

The water equivalence of a body is the body of water that has the same thermal capacity as the body, that is, it is the body of water that, receiving the same amount of heat, undergoes the same temperature variation as the body. Thus, we can say that water equivalent to iron is greater than copper means that when water has the same thermal capacity as iron, that thermal capacity is greater than that of copper.

Water equal to iron is greater than cooper