Railways has introduced a new system through which you can complain in the running train about anything related to the train. This is one of the most needed service to improve railway services.
Make sure your SMS is brief and to the point. Give the train number and write in complaints like no water in bathroom coach S10. No light, no fan with coach and berth number.
All you have to do is message to 8121281212 with the complain.
You can also complain through twitter handle of Indian railways authorities. They are very active and take action fast. You can find the twitter handle of your concerned railway region in the below image.
Hope this helps. Please do comment your complaints and suggestion. Your comments and suggetions are important for us.