My doctors give me a prescription for sterile water for irrigation 1000 ml or if you prefer it comes in 500 ml. Or I boil for ten minutes. When traveling in EU countries no prescription is needed. TSA has equipment to weigh water and with the prescription it goes as medical equipment and free. Because there is not a large demand I always pick up a full case so pharmacy isn’t stuck with partial case. Also sterile water for wounds comes in smaller vials and works too. I use Walgreens as it is Nationwide and they can pull up my subscription and fill as I need it.