Precaution steps:There are few precaution steps are needed during the experiment. The bottles for experiment are ensured completely full of water and no air bubbles remain to prevent the bottles contain oxygen gas. This experiment requires the use of hazardous components has the potential for hazardous reaction. Phosphoric acid is extremely corrosive to eyes, skin and other tissue. Winkler solution contains magnesium hydroxide and iodide solution and is also severely corrosive and strongly alkaline. Gloves must be wore to avoid accident. From the experiment, the titration for waste water cannot be fully discharged. This is due to the sedimentation of particles, for example soil. We must be noted the first reading when the solution become colorless.

Conclusion: Waste water have high concentration of oxygen in water than tap water.