Off my head, this institute seems relevant:
www.ihph.de/english/

Thanks Florian for your kind suggestion. It is very worthwhile for me. Actually, I plan to apply DAAD scholarship and I am now trying to prepare research proposal myself, however I did not find any supervisor for my research field yet.
Best regards and thanks,
Shane

Hi Shane,

you will have to do some research to find Universities and Profesors/Researchers that are active in the field you are interested in. Then you need to contact them directely. You can either propose them a research topic you want to do, or ask them if they have a PhD position upcoming. It also depends of the financing, if you need to a paid PhD position, you'll need to find an open position. If you can finance your life in Germany yourself (there are nornally no tution fees), it will be more easy to find someone supervising work proposed by yourself.

A good start to more info is the DAAD website: www.daad.de/deutschland/promotion/phd/en/

Best, Florian

Respected Sir/Madam,
I am Shane from Myanmar. I completed my first degree (Bachelor of Medicine and Bachelor of Surgery, University of Medicine, Magway, Myanmar) in 2008 and master degree (Master of Science in Food Engineering and Bioprocess Technology, Asian Institute of Technology, Thailand) in 2014. My master thesis was about microbial quality of water. I would like to study PhD degree (water and health) in Germany but I do not know how to find supervisor for my study. So, I would very appreciate if someone can suggest me.
Thanks in advance.
With respect,
Shane