Living water is a biblical term which appears in both the Old and New Testaments.
In Jeremiah 2:13 and 17:13, the prophet describes God as "the spring of living water", who has been forsaken by his chosen people Israel. Later, the prophet Zechariah described Jerusalem as a source of "living water", "half [flowing] east to the Dead Sea and half of it west to the Mediterranean Sea, in summer and in winter" (Zechariah 14:8). The Pulpit Commentary notes that the city of Jerusalem "was, as we know, abundantly supplied with water by many conduits and subterranean channels; but standing, as it does, surrounded by hills higher than itself, it is physically impossible that the waters could literally flow as stated. The description is symbolical…"
In John's Gospel, the phrase is attributed to Jesus speaking with the Samaritan woman whom he meets at Jacob's Well in Sychar:
"If you knew the gift of God and who it is that asks you for a drink, you would have asked him and he would have given you living water" (John 4:10).