Under the New Covenant, every child of God has the Spirit of God, on the inside. This is automatic. There is however a difference between being born of the Spirit and being filled with the Spirit. The born again Christian can thus be full of the Spirit of God that he/she has received. Just the same way a jug can have water but will still not be full. There is a capacity for fullness, but the jug only has some water in it. It’s the same way when we’re born again. We have the Spirit, but we are not full of the Spirit.
In Acts 2: 4, the Bible records that they were all filled with the Holy Ghost and began to speak in other tongues as the Spirit gave them utterance. So we can say, speaking in tongues is evidence of being filled with the Spirit.
The Bible uses water a lot when talking about the Spirit of God. In John 4: 11 – 14 when speaking to the Samaritan woman, in verse 14 especially, He said, ‘But whosoever drinketh of the water that I shall give him shall never thirst; but the water that I shall give him shall be in him a well of water springing up into everlasting life’. This water is the spirit of God that leads to eternal life.
Also, in John 7: 37 – 39, speaking about the Spirit, Jesus said if any man thirst let him come unto me and drink and if we believe on Him, out of our bellies shall flow rivers of living water’.
Now, these two verses refer to two different experiences. The New Birth is a well of water in you springing up to eternal life. Your own eternal life. The infilling of the Spirit is rivers. Rivers flowing out to others to bless.