In the Chinese Mahayana Practice, there is this ritual of invoking blessed water through recitation of the Great Compassion Mantra.

This mantra is closely related to the popular Bodhisattva of Compassion. Kuan Yin.

The blessed water is being drank by devotees to seek blessing or given to the sick .or anyone suffering from spiritual disturbance.

Pre-requisite

The person invoking and consuming the water must have faith. (The mind plays an important role)

The person invoking the blessed water should be someone with compassion.

That person should not have committed grave faults such as killings etc. Basically, someone who observe the Buddhist precepts.

How to invoke the blessed water.

Prepare a glass of clear water

Step 1 – Recite refuge prayer

Step 2 – Invoke the blessing of Bodhisattva of compassion, Guanyin by thinking about this Bodhisattva and praying for blessing

Step 3 – recite the great compassion mantra in front of the water

Step 4 – state the reason for invoking the blessed water

The water can be consumed.

The Great Compassion Mantra
Namo ratnatrayaya.

Namo aryavalokitesvaraya.
Bodhisattvaya.
Mahasattvaya.
Mahakarunikaya.
Om.
Sarva abhayah.
Sunadhasya.
Namo sukrtvemama.
Aryavalokitesvara garbha.
Namo nilakantha.
Sri mahabhadrasrame.
Sarvartha subham.
Ajeyam.
Sarva sattva nama varga.
Mahadhatu.
Tadyatha.
Om avaloke.
Lokite.
Kalate.
Hari.
Mahabodhisattva.
Sarva sarva.
Mala mala.
[Masi] Mahahrdayam.
Kuru kuru karmam.
(Kuru) Kuru vijayati
Maha vijayati.
Dhara dhara.
Dharin suraya.
Chala chala.
Mama bhramara.
Muktir.
Ehi ehi.
Chinda chinda.
Harsam prachali.
Basa basam presaya.
Hulu hulu mala.
Hulu hulu hilo.
Sara sara.
Siri siri.
Suru suru.
Bodhiya bodhiya.
Bodhaya bodhaya.
Maitreya.
Nilakantha.
Dharsinina.
Payamana svaha.
Siddhaya svaha.
Mahasiddhaya svaha.
Siddhayogesvaraya svaha.

Nilankantha Svaha

Varahananaya Svaha

Simhasiramukhaya svaha.
Sarvamahasiddhaya svaha.
Cakrasiddhaya svaha.
Padmahastaya svaha.
Nilakanthavikaraya svaha.
Maharsisankaraya svaha.
Namo ratnatrayaya.
Namo aryavalokitesvaraya svaha.
Om siddhyantu.
Mantrapadaya svaha.

Side note

There was study conducted by a Japanese researchers on the power of prayers on water. He tried to see if there’s any effect on the water by using modern technology.

Here’s a link.

http://www.masaru-emoto.net/english/water-crystal.html