The incident which you have mentioned is little bit strange. I am not able to understand why these people are doing this with you? Is there any other reason? Why they are behaving indifferent with you?
What I think is that initially as you are new in that family so you need to be little cautious with you behavior. Try to make yourself adjustable with them.
I have observed that old people are hungry of honor and praise. If you start saying that “yes mother you are absolutely right” then she will be happy. Praise her time to time like “your experience is very valuable for me”. If she is saying that you are wasting too much of water then agree with her. Say her that “I am trying to learn that. Please guide me to work efficiently”.
When you do this your mother in law will start thinking that you are accepting her knowledge. Which will feel her good. As time will pass she will become relaxed with you. I have practically seen this. One of my khadoos aunty has been handled same way by her daughter-in-law.
Your sister-in-law is not a problem for you. One day she will have to leave her home..So don’t take tension for her.But as your husband is only listening to them and not applying his mind so right now don’t go against her. You can take revenge with her later (just joking)
I think in a new family to adjust you should swing in the direction of water . Don’t try to point out wrong thing. Because this will create unnecessary wrong impression about you. Try to follow their instructions for sometime. Later you will feel that these people will start accepting you. Then you can put your points also.
Try this and see the results. But one important thing. Don’t loose your heart. Every problem comes up with a solution.