The giant oil slick that has disrupted life along the Ohio River since Jan. 2, when an Ashland Oil storage tank collapsed in Pennsylvania, continued its slow flow through West Virginia. Federal Environmental Protection Agency officials said the leading edge of the spill was about 15 miles down river from the Tyler County town of Sistersville. The town of 2,300 has been conserving water by closing car washes and taking fewer showers, while schoolchildren have been drinking bottled water. The town's 440,000-gallon storage tank has been kept filled by pumping water from barges. Bob Forester, assistant emergency services director for Tyler County, said the town's water plant intakes would remain closed until the peak of the spill had passed.