According to health professionals and health departments drinking from plastic or poly water tanks is not safe.
But I have drank from poly tanks for many years and it's never harmed me.
I work on a farm and have a poly water tank on a trailer that we use to water the cows and I have a separate spigot where I can get some drinking water myself.
The water tank is large enough to where I can water the cows and yet still have enough water to drink myself when I'm out in the field.
The water I put in the tank comes from my water well on my property where I get my other drinking water and the tank is clean and doesn't say potable water safe.
But it's never been a problem and you can buy plastic water tanks that are deemed and made safe for drinking water.