Police took the school employees into custody in the town of Rostaq, district administrator Moelam Hussein said.
Local health officials blamed the act on extremists opposed to women's education.
A total of 171 women and girls were hospitalized Tuesday, and four remained semi-conscious in the hospital Wednesday, Dr. Hafizullah Safi said.
Some 25 women and girls returned to the hospital Wednesday morning, complaining of more stomach pains, fever and vomiting. They were given medication and released, said Safi, the provincial health department director.
A sample of the water from the school was taken and had been sent to Kabul for testing, but it will take several days for the results.
The victims range in age from 14 to 30 and were taken to a hospital in Afghanistan's northeastern Takhar province after their school's water tank was contaminated, according to Safi.
No deaths were reported, but more than half the victims partially lost consciousness, while others suffered dizziness and vomiting.
"Looking at the health condition of these girls, I can definitely say that their water was contaminated by some sort of poison," Safi said. "But we don't know yet what was the water exactly contaminated with."
"It is the work of those who are against girls' education and peace and stability in Afghanistan," district administrator Hussain said.
In 2010, more than 100 schoolgirls and teachers were sickened in a series of similar poisonings.
During the Taliban's rule from 1996 to 2001, many Afghan girls were not allowed to attend school, though the schools began reopening after the regime was toppled by the U.S.-led invasion.
Observers say, however, that abuse of women remains common in the post-Taliban era and is often accepted in conservative and traditional families, where women are barred from education and commonly subjected to domestic violence.
In January 2011, Afghan Education Minister Dr. Farooq Wardak told the Education World Forum in London that the Taliban had abandoned their opposition to girls' education. But the group never offered a statement confirming or denying that claim.
Female educational facilities, students and teachers, meanwhile, have come under vicious attack as the insurgency has spread outside Taliban strongholds in the southern provinces of Kandahar and Helmand.
The country maintains one of the world's youngest populations. Officials say literacy rates among both children and adults remain low.
