They're widely available too. If you're going away for a while, you could consider taking a bottle of Milton sterilising fluid instead. You'll also need some plastic syringes too, which your GP or pharmacist should supply you with. Adding vitamin C to your chlorine-sterilised water makes it a whole lot better. You can get a second set of tablets to add which do the trick, or squeeze some orange juice in it.
Iodine tablets are more effective than chlorine, killing cysts too.
Iodine shouldn't be taken if you're pregnant. Follow the instructions for the tablets you are using. If the water is very cold, allow double time. You can persuade a condom to hold a litre of water without too many problems. You can read more about this survival kit elsewhere on the site.