DIY- Roach Spray - Soap and Water is an effective method of killing roaches is with soap and water. Mix 1 cup water with 1 tsp. of soap. Pour the solution in a spray bottle, then spray it on roaches. The soap solution will suffocate them as the suds block their pores and prevent breathing. Use this homemade roach killer as often as needed. You may also leave a jar of water near the corners that they frequently visit. When they crawl into the jar, they will not be able to escape.