KABUL — Canadian soldiers at Camp Julien in the Afghan capital were permitted to take showers late Thursday for the first time since the water supply was shut down due to tampering early Monday.

Italian technicians determined a foreign substance found in the camp's 55,000-litre holding tank during a routine filter change Sunday night was likely soap or a cleaning fluid and not any biological or chemical agent. A military police investigation was underway. The water system filters from the holding tank into four large bladders. Only two were affected.

The system was shut down at 8:30 a.m. Monday after most of the camp's 1,700 civilian and military residents had completed their morning routines. Laundry services were also affected at the camp in the southwest corner of Kabul.

Col. Alain Tremblay, commander of the 2,100-member Canadian contingent that is part of the 32-country NATO force in Kabul, has said it's unlikely that the contamination was an accident.

But he added that he believed the incident was an act of "fool's play" rather than malicious sabotage. "I think it's a very bad joke," he said.

Civilian employees isolated the problem soon after they found a frothy, "soapy-like" substance on top of the water when they were changing filters.

No one was reported sick due to the incident, officials said. Rudimentary chemical tests initially conducted by medical staff on the base later confirmed the material was non-toxic.

Canadian soldiers and civilians at Camp Julien drink bottled water imported from the Persian Gulf, but there are plans to start bottling their own water.

Tremblay said the camp would maintain a backup supply of bottled product in case problems arise again.

The water felt "slippery" and contained phosphates, a soap product, said the camp's head engineer, Maj. David Lauchner.

The system was purged and cleaned and the well water was tested, but showers and laundry remained off-limits until the Italian engineers at Kabul Multi-National Brigade headquarters on the other side of town conducted biological tests that required several days for cultures to grow.

By Thursday night, authorities still didn't know why the system was tampered with, or who did it, but Tremblay had said it was "unlikely a deliberate incursion into our perimeter."

Lauchner said new precautions are being introduced at the water site, including fencing.

Camp Julien is the main base for Canadian troops serving with the NATO-led International Security Assistance Force in Kabul. A few hundred more Canadians are accommodated at another NATO base in Kabul.