Here is the short answer, if you live in the US, Canada, or Europe, I KNOW you can obtain these over the internet. I have used them on three Caminos. They are so good that people stop me to ask about them.
Here is the product:
http://www.niteize.com/product/Drink-N-Clip.asp
I recommend buying at least four for each person. They weigh "virtually nothing" LOL.
They are available at many places online, and cost about USD 4.00 each. Do a Google or Bing search. You will find a vendor that suits you. In the EU, I know they are available online. A fellow pilgrim from the Netherlands found them on the web last summer and was thrilled. I recall they were EU 3.50 each, about the same as in the US.
The first time I used these, I found that a rubber band, doubled or tripled, or more, around the bottle throat would vastly improve the clip's hold on a full bottle of liquid. Using the clips on the slightly larger diameter European specification water bottle usually resulted in the bottle slipping out of the clip if the bottle caught on anything, and sometimes from just bending over. A one-liter bottle weighed enough to stretch the rubber bands and the clip would slip off. So, I decided a better solution was needed. But the Niteize-Clips were the best thing I ever saw for this purpose.
Starting with my second Camino in 2014, I improved the attachment by obtaining a blister pack of #33 silicone ring sink fixings from the local Home Depot (Brico) DIY store, plumbing section, sink repair. You stretch each ring over the bottle neck and partially over the clip. That bottle is NOT going anywhere. The rings are nearly indestructible. The rings are about 3 cm in diameter, mas o menas...
This allows you to use what many of us on the forum consider the BEST water bottle, the ubiquitous .5 liter mineral or spring water bottle that comes free with the first bottle of water you buy on arriving in Europe. They are available in varying sizes. However, hanging anything much larger than a full 750 ml bottle from your harness or belt will cause other weight-related issues. For that reason I use four (4) of these .5 liter bottles distributed more or less evenly on the front of my harness. I wear two high up (chest height) and two lower down (waist belt). My brand of preference is Vittel, as their bottles seem to be a bit more sturdy.
The bottles are free, reusable, and when they get too "icky" for cleaning and reuse, can be appropriately recycled. I typically buy four at the beginning and use them, for the month or more that I am on Camino. When I enter a town, if I want to refill them with spring water, I buy a large 3 - 5 liter jug as it is cheaper. I refill my carry bottles and use the rest of the water for my drinking and hygiene needs. If you are able to rely on the local water source, go for it. Just rinse and refill as needed.
I hope this helps...