There are several methods to carry your water with you. Whatever you pick, keep a few things in mind:
We never carry more than 1.2 liters per person. You really don’t need to take more unless you are certain you will be doing a long stretch that will have you walking for more than 4 hours in the middle of nowhere.
There are several systems out there and we’ll highlight the most common ones so you can decide for yourself:
Before you start your trip fill your bottles with hot water (not boiling) and drop a cleaning tablet in it. Follow the instructions for use of the tablets.
You can also throw in one of those tablets that are used to clean false teeth (steradent) or use a solution with vinegar.
We find the tablets most useful because it is easy to just take a few with you in your backpack.
Thoroughly rinse the bottles with clean water and you’re all set.
During the hike you can repeat the process once in a while and we do recommend to rinse the bottles anyway before re-filling them. You can use a plain odor-free washing solution to rinse them more frequently, but we only used the tablets before and after the hiking period and plain water during the hike, without experiencing any issues.
As for regular tap water in Spain: it is fully safe to drink it. Yes, it might have a different taste than you are used to at home since there are places where they add maybe a bit more chloride or other substances. If you don’t like the taste just buy mineral water.
Pick the drinking gear that works best for you.
Think about how you are going to keep it hygienic before you buy.
Keep the system clean and bacteria-free.
Think about the environment you are walking in and if you use plastic bottles anyway: don’t throw them around in nature. Dispose of them in a correct way so they can be recycled.
Don’t carry more water around than you need.