Can i pack cold brew in a high quality PET bottle? Or must it be in a glass bottle? Also, must filtered water always be used for cold brew? Or clean tap water can do the job?
This question differs greatly on a couple key factors. First, whether it is just for your own use, and second, how long you want to keep it for.
If you are drinking this yourself, you can make it and bottle it however you like. Whether that means doing what is easiest with what is available or going all out and buying supplies, it's up to you. If you are giving it to others or possibly selling it (your question is pretty ambiguous), then you want to try and create the most delicious cold brew you can at the most economical price. Glass definitely looks a lot better, and as I will talk about next, brings better flavour when kept refrigerated.
If you want to drink it the day or two after you make it, then a plastic bottle is probably fine, but the main difference is how well the bottle keeps out light, and lets out air. It may seem as though plastic is completely air tight, but there can be gases exchanged through plastic that can change the composition of the coffee chemistry. If you want a liquid to stay fresh for longer, glass is always a better bet than plastic.
Can i pack cold brew in a high quality PET bottle?
You CAN make cold brew however you want. Tap water and PET bottles are fine for easy home brewing. It is, however, widely acknowledged that water plays a much more vital role in coffee brewing than previously thought, and when your coffee grounds are in contact with water for many hours as is the case in cold brew, you can suffer from that. Good water and glass bottles will always be better than tap water and plastic bottles.
i personally use either bottled 'SmartWater' or an additive known as 'Third Wave Water' It is the added minerals that make it good.
A PET bottle: for consumption that day - no problem IMHO.