In temples, Devotees often receive 'teertham' which comes in various forms. Sometimes it is just plain water mixed with camphor or at times it is something as rich as 'pachamrut'. What does it signify? And is there a specific gesture in which devotees have to accept it?
Theertham is usually the water with which the deity has been washed, or done 'abhishekam' with . It can contain tulsi (Basil leaves), sometimes milk, sometimes camphor and water. Hence usually, it is interchangeably used with charnamrit.
One has to receive it with both hands, and avoid spillage on the ground, as it is assumed to be holy.
It sure has a Scientific significance behind the teertham being distributed in a temple.
The architecture of any temple is in such a way that it satisfies the Shilpa Shastras and Vastu Sastras.
The foundation of the temple is usually laid out by burying copper/metal plates. The same can be observed when the idol in the inner sanctum is placed after a lot of poojas get conducted. And this is called the Consecration of the temple. Now when you walk out of the inner sanctum and look up to the central Spire of the inner sanctum, you will notice that it has the very top of the Spire is aligned with Kalashas. The Kalashas are also made up of metal, possibly Panchaloha.
The answer to this elaborate puzzle is that the foundation and architecture of the temple enhances the magnetic field surrounding the temple. Bigger temples have a much stronger magnetic field surrounding it. The central idol of the temple increases the concentration of the magnetic field into the small area of the place of idol that has been placed, as it conducts the magnetic field through the Kalashas above and the Consecration plates below.
The priest chants a lot of mantras when washing/performing abhishekam on the idol. The mantras further resonate with the idol and the inner sanctum of the temple. Hence the liquids poured on the idol is magnetically charged to the maximum due to all the above procedures.
Such highly magnetic substance when distributed to devotees will enhance their physiological well-being, literally. This is also the reason as to why teertham is usually only given in very small quantities, as it can have adverse effect on the health of a person if consumed beyond limit.
According to one's samskara balam (strength of character), he relates himself to god like father/mother, son/daughter, guru, or friend. Anything offered to God has significance in its own way. Abhishekam is one of the known easiest way to please Him or care for Him.
Teertham has become holy since it has touched the body of the god while holy mantras are being chanted. It can also be seen as one of the medium to receive divine positive energy.
Teertham is a (herbal) medical composition for health benefits
Teertham is special because of the purpose of abhishekam like for health, wealth, peace of mind, removal of sins; different liquids like coconut water, milk, honey, rose water are used.
Mantra that is chanted while distribution/consumption of teertham is:
Akala mrutyu haranam, sarva vyadhi nivaranam
samastha papa kshaya karam, Sri Lakshmi Narayana padodakam pavanam subham.
Which translates to The power of the teertham is to free you from untimely death, all forms of disease and from all sins.
Theertham is commonly available prasadam because of its ease of distribution & consumption. All other forms of prasadam are offered to Him and taken by us. Further reference on Quora is here
Because of its holiness, one has to take it with one hand folded enough to make well into which teertham can be poured and with other hand supporting below it to prevent spilling.