Jalabhishek(water offering) appeases Lord Shiva and makes all the wishes come true. According to legends, during sagar mathan a very deadly poison emerged from the depth of the sea. This poison could destroy the whole creation of God.
Lord Shiva drank that poison in order to save the world. Although, he did not let the poison reach his stomach but he still felt the side effects of the poison. He felt as if he was on fire. This is why offering water to Lord Shiva is considered good.
Neelkanth feels pacified and cared for.
Offering water to Lord Shiva appeases him and helps us attain 'moksha'. Water represents knowledge and ignorance is considered the reason behind the cycle of birth and death.