Activated carbon filters are very effective at removing many chemical contaminants from water, but they are not particularly suitable for removing nitrate (NO₃⁻). Activated carbon works mainly through adsorption, meaning it binds molecules such as chlorine, pesticides, solvents and organic compounds to its surface. Nitrates, being inorganic ions, are not adsorbed efficiently by activated carbon.

There are other, more effective methods for removing nitrate from water:

1. Reverse osmosis: this method filters nitrates from water very well. Water is forced through a semi-permeable membrane that retains most dissolved salts and contaminants, including nitrates.

2. Ion exchange resins: these resins exchange ions such as nitrates for less harmful ions, usually chlorides or sulphates. This method is widely used for the denitrification of drinking water.

3. Distillation: heating the water and then condensing the vapour removes many dissolved substances, including nitrates.

So if you want to remove nitrate from your water, you should consider either a reverse osmosis system or an ion exchange system. An activated carbon filter is not suitable for this purpose.