I tend to use a fair bit of water due to the fact it tends to whizz through the filter so quickly it doesn't seem feasible that it'd bring all the codeine with it otherwise. At least with the method I have used thus far (pouring water through the powder in the filter rather than combining them first). As long as the water is cold enough to stop any significant amount of paracetamol being dissolved I'm not sure I see an issue with how much water is used other than having less to drink if you object to the taste really.
Evad: I had a go using the recommended method - mixing water and powder before filtering. Didn't seem to make any difference really. Other than making it a bit more fiddly to get it all into the filter cos it tended to stick to the sides of the pot I mixed 'em in so needed to swill it out a coupla times to get it all in. To be honest, it actually tasted like more paracetamol ended up in the end product to me. Quite possibly just need to work on me technique but unless there is a clear reason to use that method over what I was doing before I'm tempted to stick with what I know, to be honest. Is the recommended technique recommended for safety, practicality, convenience or some other reason?