If Tom drank 200 milliliters of water from the 1 liter in the water bottle, you can convert 200 milliliters to liters to make the calculation easier.
200 milliliters is equal to 0.2 liters (since 1000 milliliters equals 1 liter).
Now, subtract the amount Tom drank from the initial amount:
1 liter - 0.2 liters = 0.8 liters.
So, there are 0.8 liters of water left in the bottle.