1. Water pollution, which is becoming more and more serious, causes illnesses like typhoid, and dysentery. (which+V]
2. Promotions should be given to employees who devote their time and efforts to us the most. (who)
3. Experienced workers prefer to work in big companies, where their salary is better and work is less. [where
4. Mobile phones which are widely used all over the world,  have an adverse effect on our mental health. (which+S+V}
5. Youngsters whose knowledge are usually not as wide as the olders, tend to commit more crimes. [whosej