Precautions for foreigners traveling to Mumbai during monsoons – Our Travel Expert opines!

I think malaria prophylaxis especially those traveling from non-endemic countries is a must.
Additionally, I think a typhoid shot, Hep A if not already vaccinated, the usual precautions about water (including hidden items like ice cubes, chutneys etc).
Definitely, high quality rain proof gear, keep an eye out for significant high tides (anything > 4.75 m is significant which in combination with significant rainfall will result in flooding of low lying areas, that the person must avoid).
He/She should totally avoid street food (though it is the month of Ramzan and quite interesting street food is available) as food tends to decay rapidly.