Activated Carbon beads 

filter and improve the smoke quality.  It is washable and freezable,.  It can be use dry or wet.  it can also be flavored.

Also, study shows that when use the carbon beads, it reduce 80% of the tar so you do not have to clean your water pipe so often.  

PS>  to Clean, simply place the beads under the sunlight, or place it in the oven.  the heat and light will detox it.