In order for roaches to die, they have to come into contact with a sufficient dose of insecticide. The challenge is how to get the insecticide to the roaches given that they like to hide away most of the time, especially when you are around. The most common method of controlling roaches in the home is the use of aerosol sprays. The typical aerosol spray available uses a water-based delivery system. This helps keep the product cost down. A water-based product is not very good at penetrating deep into cracks and crevices to kill roaches where they hide. Also, these products tend to use messy chemicals which leave a sticky residue on surfaces in your home. And then there is the smell. The bottom line - water-based products are cheap but they do not work very well and are messy.