The main differences between OPTI Water Filter and ZeroWater is that OPTI allows beneficial trace minerals to pass through while still removing the contaminants. Please keep in mind that if you are using a TDS/PPM meter to test OPTI's water, it will show up very high due to the mineral content NOT contaminants.A TDS/PPM meter measures ALL total dissolved solids (like minerals), but does NOT measure chemicals like pesticides and such. OPTI also has a higher filter capacity (120 gallons & 200 gallons per filter) and will also OPTImize your water and provide you a higher pH level than ZeroWater.