I have got a mechanical water meter which is not integrated into HA yet.
However, I got some stats from domestic water provider below.
Is there a way, to add those values to HA and get similar graph?
Use an input number helper. You can graph them.
@tom_l created the helper as you suggested and set it to 53, 52 and 84.
How should I set periods of the measurements or the month when the measurement was taken?
An example 53 should be correspond to 08/2019, 52 to 08/2019, etc
You can only record them on the date you enter them.