The study of Hydrilla (Hydrilla verticillata) effectiveness in water treatment was investigated using completely randomized designs with 4 Hydrilla densities: 0 (control) 30 50 and 70 plants. Each plot was experimented in round cement tanks added with sandy clay on the bottom. Fifty liters of canal water was then filled in. Along 6 weeks of the experiment each tank was aerated with no water exchanged. Results showed that there were no significant differences in values of temperature pH dissolved oxygen conductivity alkalinity hardness nitrite ammonia phosphate and biochemical oxygen demand in every treatment (p > 0.05). However the experimental plot with 50 hydrilla plants showed the best tendency in eradication of phosphate and improvement of biochemical oxygen demand at 86.00 and 45.73 percent respectively. On the other hand the experimental plot with 70 hydrilla plants showed the best tendency in eradication of ammonia and nitrite at 65.00 and 66.66 percent respectively.