Here is the entire context. Jesus is basically explaining the differences of physical verses spiritual. He uses water as a metaphor. Pay attention that he says you must worship in spirit.
John 4:7 (NKJV) A woman of Samaria came to draw water. Jesus said to her, "Give Me a drink."
8 For His disciples had gone away into the city to buy food.
9 Then the woman of Samaria said to Him, "How is it that You, being a Jew, ask a drink from me, a Samaritan woman?" For Jews have no dealings with Samaritans.
10 Jesus answered and said to her, "If you knew the gift of God, and who it is who says to you, `Give Me a drink,' you would have asked Him, and He would have given you living water."
11 The woman said to Him, "Sir, You have nothing to draw with, and the well is deep. Where then do You get that living water?
12 "Are You greater than our father Jacob, who gave us the well, and drank from it himself, as well as his sons and his livestock?"
13 Jesus answered and said to her, "Whoever drinks of this water will thirst again,
14 "but whoever drinks of the water that I shall give him will never thirst. But the water that I shall give him will become in him a fountain of water springing up into everlasting life."
15 The woman said to Him, "Sir, give me this water, that I may not thirst, nor come here to draw."
16 Jesus said to her, "Go, call your husband, and come here."
17 The woman answered and said, "I have no husband." Jesus said to her, "You have well said, `I have no husband,'
18 "for you have had five husbands, and the one whom you now have is not your husband; in that you spoke truly."
19 The woman said to Him, "Sir, I perceive that You are a prophet.
20 "Our fathers worshiped on this mountain, and you [Jews] say that in Jerusalem is the place where one ought to worship."
21 Jesus said to her, "Woman, believe Me, the hour is coming when you will neither on this mountain, nor in Jerusalem, worship the Father.
22 "You worship what you do not know; we know what we worship, for salvation is of the Jews.
23 "But the hour is coming, and now is, when the true worshipers will worship the Father in spirit and truth; for the Father is seeking such to worship Him.
24 "God [is] Spirit, and those who worship Him must worship in spirit and truth."
25 The woman said to Him, "I know that Messiah is coming" (who is called Christ). "When He comes, He will tell us all things."
26 Jesus said to her, "I who speak to you am [He]."
To give an idea of what he means by spirit, we can look at Luke.
Luke 24:39 (NKJV) "Behold My hands and My feet, that it is I Myself. Handle Me and see, for a spirit does not have flesh and bones as you see I have."
And here again in Acts we learn that you can not worship God with your hands or anything made by them, you must worship God in spirit.
Acts 17:24 (NKJV) "God, who made the world and everything in it, since He is Lord of heaven and earth, does not dwell in temples made with hands.
25 "Nor is He worshiped with men's hands, as though He needed anything, since He gives to all life, breath, and all things.
26 "And He has made from one blood every nation of men to dwell on all the face of the earth, and has determined their preappointed times and the boundaries of their dwellings,
Acts 7:47 (NKJV) "But Solomon built Him a house.
48 "However, the Most High does not dwell in temples made with hands, as the prophet says:
49 `Heaven [is] My throne,
And earth [is] My footstool.
What house will you build for Me? says the Lord,
Or what [is] the place of My rest?
50 Has My hand not made all these things?'