Tbh I dunno how a water pipe would work as I've never used one.
... And you don't technically even 'smoke' your opium since it's not incinerated like tobacco. It would be more accurate to say you 'inhale' opium as the process is one of vaporization.
For the most accurate depiction accessible online, (which saves me having to go into lengthy explanations which STILL wouldn't have you doing it correctly 'cause this is a technique you really have to SEE and BE SHOWN in order to learn yourself), look up ' Steven Martin smokes opium in Bangkok'.
This guy was pretty much the last non - Asian true expert who knew the craft inside out. I've learnt what I know from mostly his descriptions plus having had the extraordinary fortune of making friends with a fellow student from Laos at university, whose uncle just so happened to have operated one of the last traditional opium dens before they were all declared illegal. Said flatmate also used to work for his uncle as an assistant, preparing opium 'pills' ready for the customer to smoke; and was willing to show me.