An Achamana is a purificatory ritual that consists of sipping small amount of water from right palm after sanctifying it(the water) with mantras.
An Achamana precedes all Vedic ritual.
There are certain rules which are needed to be followed while doing it.A recommended posture for doing it is the squatting position(although i don't think that this is mandatory).
From this page:
- Achamanam Sipping water sanctified by mantras
Sit in a squatting position, facing east or north. The hands should be between the knees. Bend all the fingers other than the thumb and the small finger slightly so that a hollow is produced in the palm. Take a very small quantity of water in the palm and sip, uttering the following three mantras (one sip for each mantra):-
Achyutaya namah Anantaya namah Govindaya namah
Question-Why it is important to squat while performing an achamana?What are the advantages of squatting(in this regard) over any other postures like say Sukhasana or Padmasana?