Can my iPhone really be fixed?

A few days ago, it rained really hard, I was cycling at the time and had my iPhone in my rucksack. When I got home it was drenched. I have only had it 2 months, I was really upset.
Anyway, I sent it to someone to be repaired. It only cost £10. He said it is working perfectly now, although he did have to replace the battery.
Can a water damaged iPhone really work perfectly again?