IIRC, this is going to depend on what cuts are being used, if you are buying large bags of fairly pure heroin, or with a predictable cut you can work around - its not going to make much of a difference. I don't know many junkies who can do molar equasions, but its not a big deal so long as you add a little salt or use sterile saline to mix. Cigarette filters worked OK for me in my brief needles phase. Now, the flipside, when your dealer is selling you stepped on little balloons with all kinds of different soluable adulterants, to be frank, beyond the molar absorption into pure neutral water, all more liquid esp. warm liquid or liquid with various chemical treatments is going to do is suck up a ton of gunk you really don't want. I'm not particularily into heroin, and I get kind of suspicious with heroin addicts who are doing little baggies cut with insoluable crap where the point is more the dealer making money and doing everything he can think of to make the junkie feel sick (and work harder to get more heroin). So, really this issue does have two parts - if its cut with a potentiator then maybe a little more water will work. Really the key factor is just how efficiently it will cross the BBB, just like using MSM or DMSO with ketamine - a perfectly acceptable cut because it maximizes the dose. With heroin though, I suspect a fair number of cuts are such that its barely going to cross the BBB and just end up clumping in eddies in the cilculatory system and ending up in tissue. Then again, its my opinion that for safety's sake you should either stick to morphine in a sterile container or plug heroin, its just not worth it to ruin your circulatory system. Alot of drugs are harmful, but the harm is fairly short lived - in 7 years your body basically regenerates - but a destroyed circulatory system does not. Are you getting high to have fun? or just because your dealer has put so much poison in your dope that you don't care anymore because you have no hope?