I support
@Rodrigo Cerqueira's campaign. I'm aware of the plastics litter in the oceans, of plastic micro-particles, of the litter problem on and off our public places. I own about 5 Sigma bottles of various sizes and have used them on many treks. At the risk of being ostracized forever: I don't take them with me on the Camino. I do refill empty mineral water bottles with tap water from time to time. Most of the time, I don't like the taste of tap water. Yes, I do know that other people don't get this. So I do buy mineral water in plastic bottles. Admittedly, I've not sampled water from every tap along the CF (no idea about Portugal) but the only one that tasted really really good to me was the one from the spring below the picnic area on the other side of the road at the Cruz de Ferro.
My town hall administration has recently introduced household waste bags for plastics only. I'm amazed/horrified how much of our household waste is plastic: plastic wrappings for cheese, ham and sausages, plastic boxes for fruit and vegetables, joghurt containers, small clear plastic bags for all sorts of food items, the list is endless. I've not actually measured it but it seems that all this stuff creates more waste volume than the empty mineral water bottles we dispose of (incidentally in a
different household waste bag).
I've not really looked into the science and recycling methods but know that commercially sold mineral water bottles are PET bottles nowadays.