Water bong designs are primitive and are used as inefficient liquid based semi-permeable smoke particle filters.
When a bong is used the hot cannabis and tobacco smoke particles are pulled down from the bowl and through the filter water. Water immersed hydrophilic air cavitation bubbles are formed at the end of the downstem which rise to through and to the top of the bong's filter water. The outer skin or nuclei of the water immersed hydrophilic air cavitation bubbles keep some smoke particles suspended in the air cavitation. Some of the particles will merge into the cavitation's nuclei where they are then dispersed into and on top of the filter water.
Filtering any kind of smoke through a water filtered bong is inefficient. This inefficiency is caused by the large amount of particles that remain suspended in the water immersed air cavity bubbles that pass through the water. These open flow, suction powered water bongs are not designed to filter every particle from the smoke that travels through them. If every particle that travelled through the filter water were caught, then the bong wouldn't be useful for burning and smoking weed or tobacco.
Each form of consuming weed is different in potency and efficiency. Each of these forms can be ranked from weakest to strongest. The weakest and most inefficient forms of consuming weed are: eating raw cannabis buds or leaves and smoking a water bong. Stronger forms include: absorbing or ingesting weed oil and smoking a weed joint. The strongest and most efficient form of consuming weed is vaporizing weed concentrates using no filtration.