Water filter?

Not sure why they telling you to buy water....you can save a lot.
There are many on the market they all do more or less the same thing.

I would get one of those clay pot type filters , just search clay filter to see what I mean. I like those the best. The cheaper plastic ones you fit on your taps break after about a year usually

One of the biggest lifestyle changes I've seen in Brazil is that everybody used to use those clay pot filters that Stevefunk recommends, and now, practically nobody does.  They're not easy to find anymore.
Countertop water purifiers range in price from ~R$100 to ~R$900, and all do about the same thing.  Check a couple of appliance stores; focus on energy efficiency, throughput, and availability of replacement filters, because you will need to replace filters regularly.
Are you sure you need one?  São Paulo is very proud of the quality of its water, and for most cooking, the water ends up boiled anyway.  We ended up getting a column-type water cooler for drinking, because it doesn't take up counter space.  Bottled water here in Manaus costs R$6,00 for 20 liters, so there's not a huge saving in "rolling your own".

- " so there's not a huge saving in "rolling your own " What about saving the environment and not producing so much plastic junk.....

The clay filters are easily found in any department or hardware store in São Paulo
Try Leroy Merlin

The 20 l jugs are recycled again and again, so I repeat, savings are minimal.  But admittedly, my views aren't informed by a particular ideological commitment to outmoded technology.