People have to understand the importance and meaning of Barakah first. The Prophet said: " The most sublime of all earthly waters is that of zamzam; therein one finds food for the hungry and medicine for the ill." [ At- Tabarani ] Now do anybody who calls oneself a Muslim doubt the above statement? How many times did poison become medicine due to barakah, How many times Allah Ta'ala has made simple things to do miracles? Arsenic or no arsenic, taste difference, toxicity etc etc. Whatever might be the outward findings. ZamZam is the best of all earthy waters. Period.