Bring water to a gentle boil in a non-reactive pot or pan.
Optional: Crush the cumin seeds with a rolling pin or in a mortar pestle. The idea here is to release their flavor and volatile oils. You don't need to make a fine powder.
Add them to the water and bring it to a boil on a medium heat.
Then reduce the flame and simmer for 5 minutes. Bring this to a boil again on a slightly higher heat and turn off.
Cover and let cool down until warm.
Place a strainer over a cup or a pitcher. Filter jeera water and serve warm or at room temperature.
If you prefer to have jeera water the entire day, then boil 10 grams of cumin seeds in 1250 ml of water following the same steps mentioned above. Strain it and drink the whole day.