This teaching can be found in Piskah 48, though with slighty different wording which is underlined below. The teaching states as follows:
“Rabbi Akiva says, ‘Behold, it says [in sefer “Mishlei”], “Drink water from your pit…”, [then the pasuk says, “…and flowing water from the midst of] your well.” (Mishlei: 5; 15) At first [the person’s Torah knowledge is comparable to] a pit which is unable to bring forth a drop of water on its own, it only contains that which is within it, such is [true of] a Torah student, who at the beginning of [his involvement in Torah study, who] has not learned everything, only possesses that which he has learned. [In referenence to one who has spent more time studying Torah, the pasuk states, “…and flowing water from the midst of your well.”, [he being] similar to a well, just as a well causes running water to flow from all of its sides, so it is [the case in reference to a person who has become familiarized with Torah knowledge who has] students come [to him to] learn from him. In this context [the pasuk] says, “Your springs shall spread [outward]…” (Mishlei: 5; 16), words of Torah are comparable to water, just as water provides life to the world, so too are words of Torah [a source of] life to the world, as it says [ in reference to words of Torah in “Mishlei”], “For they are life to those who find them…” (4; 21) Just as water raises those who impure out of their status of impurity, so too do words of Torah raise those who are impure out of their state of impurity, as it says [in sefer “Tehillim”], “Your words are exceedingly pure and Your servant loves [them].” (119; 140) Just as water rejuvinates the soul of the person, as it says [in “Mishlei”], “Cold water on a weary soul…” (25; 25), so too does Torah rejuvinate the soul of the person, as it says, “The Torah of HaShem is complete, it rejuvinates the soul…” (Tehillim: 19; 8) Just as water is free for the world, so too are words of Torah free for the world, as it says [in sefer “Yishayahu”], “Woe, all of those who are thirsty shall go to water…” (55; 1) Just as water has no finite value, so too do [words of] Torah not have a finite value, as it says [in “Mishlei”], “It is more valuable than pearls…” (3; 15)”
From the above teaching of Rabbi Akiva concerning the comparison between water and Torah, we can further appreciate concerning the countless benefits that Torah study has to offer the person and the infinite reward one can derive from Torah study, all of this can be acquired without having to spend any money.
 The pasuk from sefer “Mishlei” states, “Your springs shall spread outward, in the streets there shall be streams of water.” (Mishlei: 5; 16)
The previous pasuk states, “Drink water from your pit, and flowing water from the midst of your well.” (Mishlei: 5; 15)
RaSh”I explains on the above two p’sukim refer to Torah study, which is compared to water. The pasuk first compares the Torah that one studies earlier in life to water that is gathered in a pit and then compares it to flowing water. Eventually the person’s springs of Torah will spread outward in that he will acquire students, will teach Torah publicly, and will become well-known for the Torah that he teaches.
The MaLBI”M explains that at first the person’s study of Torah familiarizes him with the manner in which to attain wisdom and then, once the person is familiar with the teaching concerning how to amass wisdom, he then is comparable to a well and a stream who’s water spreads out, as he is able to come up with his own chiddushim (Torah insights), as well as possessing a great deal of Torah knowledge, which flows outward, in that he now benefits others from his Torah knowledge and wisdom. The pasuk quoted in sefer “Shmiras HaLashon”, first compares one’s teaching of Torah to a spring of water which “spreads outward”, in that the person at first benefits the members of his household and his students with his knowledge of Torah. The person is then compared to streams of water that flow in the streets, as his Torah teachings then benefit all of The B’nei Yisrael, similar to a stream flowing in the main streets. One’s Torah teachings that spread “outward”, according to the MaLBI”M, is like water that flows behind the houses, in an area which is only frequented by the people of the household. The “Richov” – “רחוב” – “street”, is the wide – “רחב” – main street which is in front of the houses and which is accessed by the public. The MaLBI”M explains that once the person’s Torah teachings become increasingly public, his Torah teachings are comparable to a stream which is continually strengthening and to a river which doesn’t cease from flowing. This teaching concerning the comparison of Torah to a river is found in “Pirkei Avos”, where Rabbi Meir teaches that these and other benefits come to a person who learns Torah for the proper reasons (lishmah). (Pirkei Avos: 6; 1)
 The entire pasuk states, “Fear of HaShem is pure, it remains forever, the judgments of HaShem are true, they are correct together.” (Tehillim: 19; 10) The Metzudas David explains that the judgments of The Torah do not contradict one another.
MaLBI”M explains that “Fear of HaShem” refers to those mitzvos for which the reason behind their performance is not known to people – Chukim.
In the text of “Sifrei”, instead of quoting the above pasuk, as is quoted in sefer “Shmiras HaLashon”, it quotes “Your words are exceedingly pure and Your servant loves them.” (Tehillim: 119; 140).
 The entire pasuk states, “And these matters that I command you today, shall be on your heart.” (Divarim: 6; 6)
 The entire pasuk states, “The Torah of HaShem is whole, it rejuvinates the soul, The Testimonies of HaShem are reliabe, they make the fool wise.” (Tehillim: 19; 8)
Metzudas David explains that “The Testinonies” of HaShem refer to the mitzvos, as they testify concerning those who fulfill them that they believe in HaShem.
RaDa”K explains that The Torah testifies concerning the wisdom and uprightness. The Torah is also that which keeps the person’s soul in existence.
Ibn Ezra, quoting Rav Sa’adia Gaon, explains that The Torah testifies to HaShem’s existence, as David HaMelech explains. The Torah “returns the soul” of the person, as it removes doubt from the person’s heart.
 The entire pasuk, which speaks of Torah in terms of water, states as follows, “Woe, all of those who are thirsty go to water, and those who do not have money, [will still be able to acquire water – translators addition], go acquire and eat without money, and without monetary value wine and milk [can be acquired – add.]. (Yishayahu: 55; 1)
Targum Onkelos writes the pasuk as stating the following:
“Woe, all of those who desire to learn [Torah] shall come and learn, and those who do not have money shall come and hear and learn, and shall come and hear [Torah] without [needing] money and without [expending] money he can acquire [Torah] teachings which are superior to wine and milk.”
RaSh”I notes that the word “הוי” – “woe”, is a call of invitation, in this context, to encourage people to gather together to learn Torah.
Metzudas David explains that “wine and milk” refer to all matters of wisdom of The Torah, which can all be learned without having to expend money.
RaDa”K explains that Torah is compared to wine in that wine gladdens the heart and is compared to milk in that milk is necessary for a little baby in his existence and development, so too, Torah study is necessary for the existence and development of the soul, which continues to grow in its level of learning.