New zealand must desalinate seawater to have freshwater like australia.

The statement is not true. In fact, the truth is the other way around. New Zaeland is a country that has an abundance of freshwater reserves, and considering that its population is relatively small, it has it very well in the water supply department. Australia, on the other hand, is a country very poor with freshwater sources, especially when its size its taken into consideration. Luckily for Australia it doesn't have very large population, so the problem is still not as big, though the country is gradually engaging into desalination of seawater, as in some areas there are too many people concentrated, and the water sources can not respond to the demand. New Zealand doesn't have this problem though, as the country has lot of streams, rivers, and lakes, most of which have high quality freshwater that can be used for drinking and everything else. The country needs to be careful though as the pollution is increasing, and even though it doesn't have a problem at the moment, if the current trend continues it might end up in a bad situation in several decades.