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Chicken Pox
Mumbai is a hotter place than Poland and it is best to carry tabs for Chicken pox if you are supposed to travel during Summer. Chicken pox is more common than Malaria. Unlike Malaria you may not find tablets for Chicken pox in many pharmacies particularly if you are outside the city. This is mainly due to the fact that we Indians mainly use Neem leaves to treat Chicken pox rather than using pills, particularly in small towns and villages.
Mosquitoes & Malaria
Mosquitoes will not be of much problem if you are spending most of the time in hotel and offices. Although it is best to have mosquito repellents with you.
Malaria tabs are not that much needed provided in the places you are visiting mosquitoes will be less. I live in India and I can say that it is unlikely to catch Malaria if you stay hygiene. As you can see in this WHO article here Malaria is sharply reducing in India. If you ever need Malaria tabs they are available in almost all the pharmacies in Mumbai. So it is not a big issue unless you are visiting places that are less hygiene and have mosquito problems such as slums near by water areas.
General precaution
A general precaution is to always take boiled /mineral water with you. India is a hotter place and you may need a lot of water. It is best to have boiled/mineral water with you. I suggest you to drink Boiled/Mineral water at all times possible, don't drink water from public taps without boiling though it may have a label drinking water. You can also refer this article here which says,
Most of India's tap water is unfit for consumption. Restaurants will offer treated drinking water, but itβs advisable for visitors to always drink bottled water.
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Malaria is not an extremely serious concern in Mumbai, especially if you are only going to be there a week, and the thin protection that anti-malarials give you isn't really worth the nausea they deliver much more reliably.
My recommendation for anywhere that isn't an actual swamp is DEET, a effective, long-acting insect repellent. It chases away malaria-carrying Anopheles mosquitoes and many other biting and stinging insects.
The problem is, for various reasons, DEET is not available inside India, you have to bring your own. In tropical countries other than India you can buy it at any corner shop; in temperate countries, you have to go to sporting-goods stores. I like 100% DEET formulations but if your skin is at all sensitive, buy the 25% bottle (the 7% is a waste of time, imo). Pump-spray or cream is better than powder. Put it in a plastic bag before you put it in your luggage, in case of leaks.
As Kolappan Nathan says, don't drink the water. Actually, that's probably good advice whenever you leave your home country -- you are well-adapted to the flora in your native water, but less so to foreign germs -- but it's especially true in India, where much of the water supply is contaminated with fecal matter and worse.
And bring some Imodium or buy it as soon as you land. Mumbai is the gastroenteritis capital of the universe, and you do not want to be limping to the chemist's shop after it strikes.