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

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

1. Reverse osmosis: This method is very effective at filtering nitrates out of water. It involves forcing water through a semi-permeable membrane, which 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: By heating the water and then condensing the vapour, many dissolved substances, including nitrates, can be removed.

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.