Praise be to Allah.
The scholars are unanimously agreed that it is permissible to seek barakah from the relics of the Messenger (peace and blessings of Allaah be upon him), such as his hair, sweat and other things, because there is evidence to that effect. It was narrated that Anas ibn Maalik said: When the Messenger of Allaah (peace and blessings of Allaah be upon him) stoned the Jamrah and offered his sacrifice and shaved his head, he showed his right side to the barber and he shaved it, then he called Abu Talhah al-Ansaari and gave it to him. Then he showed him the left side and said: “Shave it.” So he shaved it, and he gave it to Abu Talhah and said: “Share it out among the people.” Narrated by Muslim (1305).
And it was narrated from Anas that Umm Sulaym used to put out a mat of leather for the Prophet (peace and blessings of Allaah be upon him) and he would take a nap in her house. When the Prophet (peace and blessings of Allaah be upon him) fell asleep, she took some of his sweat and hair and kept it in a bottle, then she put it in some sukk (perfume made of musk). He [Thumaamah ibn ‘Abd-Allaah ibn Anas] said: When Anas ibn Maalik was dying, he left instructions that some of the sukk should be put in his hunoot (perfumes used in preparation of dead for burial). Narrated by al-Bukhaari (6281).
This and other reports indicate that Allaah created barakah in the person of the Prophet (peace and blessings of Allaah be upon him) and whatever separated from it of hair, sweat and so on, from which barakah may be sought and one may hope for benefit therefrom in this world and the in the Hereafter. The One Who bestows this goodness is Allaah, may He be blessed and exalted.
But the claim nowadays that this is one of the hairs or relics of the Prophet (peace and blessings of Allaah be upon him) is a claim for which there is no proof. Most of the claims that are made to that effect are lies and myths, such as their saying that this is a hair of the Prophet (peace and blessings of Allaah be upon him) because if it is placed in the sun it has no shadow. No attention should be paid to such words.
Shaykh al-Albaani (may Allaah have mercy on him) said: We know that his relics – such as his garments, hair and so on – have been lost, and it is not possible for anyone to prove that any of them exist for certain. Al-Tawassul, p. 147.
Based on this, it is not permissible to seek barakah from the water you asked about, unless it is known for certain that what was placed in it is a hair of the Prophet (peace and blessings of Allaah be upon him), but there is no way to prove that. We should beware of charlatans and liars and propagators of bid’ah, and we should acquire knowledge from people who are known to have knowledge of the Sunnah and who are defenders of the Sunnah and who strive hard to spread the Sunnah. It is amazing how a gathering to support the religion could turn into encouraging people to believe in unproven matters. It would have been better for the lecturer to call people to learn and adhere to the Sunnah, because that is one of the means of success.
May Allaah enable us and you to follow the Sunnah properly.
And Allaah knows best.