How can I ensure my prayer is accepted when I encounter impurities from a shared school bathroom?

If somehow urine splits onto my pants and then it becomes dry and then I touched that part with wet hand, is my hand impure? Again if the dry part again comes in contact with water and becomes wet and I touched it then what is the ruling? I also want to share that I live in a residential school. Here public toilets are used. Beside the toilet there is basin. Sometimes I walk and water falls on my leg while walk in from the mixture of water on the floor. What can I do? Again in the commodor it seems hard to me in case of purification. I want to use tissue paper for this. But there is scholarly difference regarding whether using water farz or not? What is the correct ruling? What should I do for this? I am very much fearful regarding the matter about my salat becoming correct or not as I fear whether I am pure or not? Please suggest me to solve my problem with Quranic verses and Hadith quotes.