There is a lot of contention in the brewing community when it comes to cooling down your wort with ice. Yes, using ice can introduce contaminants if you go about it the wrong way. But ice can be the most cost efficient way to cool down your brew wort and fast as well.
I am a hobbyist brewer and I just so happen to live in a tropical client here in Queensland, Australia. We get hot summers in the 30 – 40 Celsius range during summer, some parts even hotter. There is nothing like a nice cold glass of beer to drink to beat the heat.
To get into the safe zone for an ale style beer of around 21 Celsius, you either need to have an elaborate cooling setup or an additional fridge for storing your fermenting vessel. Yes, you can get cooler bags and even wrap a wet towel around, but honestly, it is a lot of work and can be more costly than some hobbyist brewers like myself can justify.
Now back to the ice.
The quality of store bought ice is quite high. The chances of it contaminating your brew are no less than you contaminating it with your finger or improperly sterilising your equipment. I know some people use store bought ice and have great success. I personally don’t do that.
I simply fill some large zip-lock/sandwich bags with tap water. Once again another point of contention, some will only use purified and filtered water. Others will use tap water and boil it. I personally do not go to the effort of boiling it. I simply fill the zip-lock bags with water and freeze them into ice.
Once they have formed ice, break them up and put it into the bottom of your fermenting vessel. Then you pour the wort slowly over the top of the ice and top up with water. Once again, most people simply use chilled tap water or even straight tap water during this phase anyway which can be a source of contamination.
I never re-use the bags, once I freeze them once they get dried and used for food storage purposes, but I never use them to freeze water again. This ensures only new zip-lock bags are being used and I have had no problems with this approach.
If putting ice into the wort does not jive with you, you can use the frozen ice to make an ice bath and cool your wort that way.