The Senate the States House

It has bemused me for years now, how the Senate which was established under the constitution to be the States House can have ministers of government as part of it's makeup.
How on earth can government ministers being appointed from the Senate represent the state that elected them? How can a government minister act in the best interests of his/her state in the senate if she/he has government solidarity as the main aim?
For example, Water Minister, Penny Wong is a senator, and yet she does little to champion the needs of South Australia. More often than not she seems to champion Queensland and tells us why we can't have more water into South Australia, instead of demanding how we can get more water. It has rained bucket loads in Queensland you know. But it will never reach South Australia.

Premier Mike Rann is now a lost cause and has shown South Australians that we can't rely on him to champion our needs.
http://www.youtube.com/watch?v=t7NbuCsYvWw

All federal ministers should come from the lower house, and senators should do just what they were elected to do under the constitution, represent the interests of state that elected them.