You are asking a very controversial question.

My answer is the best way to go is with a distiller vs reverse osmosis or various filter cartridges.

I love this model of distiller. It is extremely reliable and I bought one for both of my sons.

The Megahome has been operating 5 days a week for > 5 years with zero problems. Read the customer reviews:
https://www.amazon.com/Megahome-Water-Distiller-Stainless-Bottle/dp/B00AKCK8NC/ref=sr_1_4?s=home-garden&ie=UTF8&qid=1471154253&sr=1-4&keywords=megahome+water+distiller

Best to you,
Grizz

Finding a company who will ship to India is going to be your biggest problem IMO. Distillation is a simple process, heat a liquid and condense the steam using a cooling method. It should not be expensive depending upon the quantities that you need and the heat source that you use. If you can use a cooker then use the largest one you can find that fits your cooker. Having an inbuilt thermometer helps so that is something to look for. Many are available from China but I think that you might be able to find one supplied from India.

You might be able to build one yourself with a bit of ingenuity if you can find a suitable large pressure cooker and fit some valves to it for steam to escape to the condenser. If you look at a few designs that are available you might be able to work out whether you could make one yourself and/or acquire the necessary parts. The condenser can be either glass or copper tube and needs to sit in a cold water source, the cooler the better in order to condense the steam. That might be where you need to consider carefully living in India where I imagine the temperatures might get hot and hotter water will mean poorer cooling and steal condensing. Maybe some combination of fridge element and water to keep it cool. It might be worth measuring your water temperature such as putting a thermometer under a running tap. Having a running water source to continually cool the steam is needed. Or use some form of fridge element to cool a water bath where the condenser is situated. That might be worth considering if the temperatures are high when you intend using it.

Only you know your local circumstances so you need to weigh up your options.

Also consider the vessel because having a high quality stainless steel vessel might make a difference as some use lower quality 304 stainless steel. However for water distillation that might not make much of a difference as water is less likely to react with even poorer quality stainless steel.

Chinese distributors seem to ship to India

http://www.ebay.co.uk/itm/25L-ALCOHOL-STAINLESS-DISTILLER-HOME-BREW-KIT-MOONSHINE-STILL-WINE-SPIRITS-MAKER-/181970407739?hash=item2a5e48113b:g:rXQAAOSw1S9Wekqs
This one is from Germany
http://www.ebay.co.uk/itm/NEW-14L-Alcohol-Stainless-Distiller-Home-Brew-Kit-Moonshine-Wine-Making-Boiler-/152201067597?hash=item236fe3fc4d:g:-twAAOSwbwlXAmwR

eBay.co.uk Search>
http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR11.TRC1.A0.H0.Xdistill.TRS0&_nkw=distill&_sacat=0