How do I restore my old WhatsApp history on another phone? My Samsung Galaxy S3 phone was water-damaged and is not working at all. Unfortunately, I didn't backup my chat history. 

I inserted my old SIM card and memory card into my friend's phone and downloaded WhatsApp. I linked it to my old number, but when I opened it, there were no contacts / chat history at all. 

Is there any way I could get back my old WhatsApp chat history? There are some important messages there.
The backup is held on your old phone. You would need to be able to switch it on to be able to retrieve it.

If you get it switched on its simply a case of copying the whatsapp folder from the old device to the new one, opening whatsapp and allowing it to restore messages from the backup.