I don't agree with the one detail that water has "a purely symbolic role." It can symbolize birth and life, of course, but there's more to water than that, both as it pertains to life on earth and from God's point of view. It has physical properties unlike any other other substance, and it can have extraphysical properties as well. At exorcisms, for example, holy water sprinkled on a possessed person causes pain in the demons within.
We know that water has a particular significance to God because it is so often mentioned in scripture. In fact, it's the very first substance mentioned in the Bible. "And the Spirit of God moved upon the face of the waters." (Genesis 1:2)
We know that God uses it to spiritually cleanse, not that he has to. Ezekiel 36:25 - "Then will I sprinkle clean water upon you, and ye shall be clean: from all your filthiness, and from all your idols, will I cleanse you."
And we know that water has such a great significance to God that there is water in heaven as well as on earth.
Revelation 22:1 - "And he showed me a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb."