Pennsylvania American Water has issued a 48-hour boil water advisory for 55 communities in Allegheny and Washington counties. An estimated 100,000 customers are affected. (SCROLL DOWN FOR FULL LIST.)Early Wednesday morning, Pennsylvania American Water reported that a first set of water samples overnight showed no sign of contamination. However, the boil water advisory will remain in effect until a second round of samples are available later Wednesday morning.The advisory applies only to drinking and cooking, not bathing or washing clothes.Residents of impacted communities should bring all water to a boil, let it boil for one minute, and let it cool before using, or use bottled water. Boiled or bottled water should be used for drinking, making ice, brushing teeth, washing dishes, and food preparation until further notice. Boiling kills bacteria and other organisms in the water.The water company said the advisory was issued as a precaution due to high levels of turbidity -- the cloudiness or haziness of a fluid caused by suspended solids that are usually invisible to the naked eye -- at the Elrama water treatment plant.Turbidity is a key test of water quality. According to the water company, turbidity has no health effects but can interfere with disinfection and provide a medium for microbial growth. Turbidity may indicate the presence of disease-causing organisms. These organisms include bacteria, viruses, and parasites, which can cause symptoms such nausea, cramps, diarrhea, and associated headaches.People with severely compromised immune systems, infants, and some elderly may be at increased risk. These people should seek advice from their health care providers about drinking water. The full list of communities is as follows:Allegheny CountyBethel ParkClairton Dravosburg Elizabeth Township Elizabeth Borough Glassport Jefferson Jefferson Hills Borough Liberty Lincoln North Fayette (Customers who get their bills from PAWC only) South Fayette South Park Upper Saint Clair West ElizabethWashington CountyAmwellAvella Buffalo Burgettstown Canton Canonsburg Carroll Township Cecil Township Chartiers City of Washington Claysville Cross Creek Donegal Township East Washington Fallowfield Finleyville Frankfort Springs Green Hills Borough Independence Hanover Hopewell Houston Jefferson McDonald McMurray Midway Monongahela Mount Pleasant New Eagle North Franklin North Strabane Nottingham Peters Township Robinson Township Smith Township Somerset Township South Franklin South Strabane Union Township West MiddletownWATER TANKER LOCATIONSFresh drinking water is available at the following locations. Customers should bring their own containers to fill up with water.Bethel Park Community Center: 5151 Park Ave., Bethel Park, PA 15102Canonsburg Dam parking lot: McDowell Rd., McMurray, PA 15317Canonsburg United Presbyterian Church: 112 W. Pike St., Canonsburg, PA 15317Carroll Township Volunteer FireDepartment: 988 Route 837, Monongahela, PA 15063Cecil Township: VFW 3324 Route 50, Millers Run Rd., Cecil Township, PA 15321Clairton Volunteer Fire Department: 551 Ravensburg Blvd., Clairton, PA 15025Dravosburg: 226 Maple Ave., Dravosburg, PA 15034Elrama Volunteer Fire Company: 17 Elrama Ave., Elrama, PA 15038Hanover Township: 11 Municipal Dr., Burgettstown, PA 15021Jefferson Hills Borough Police Department: 925 Old Clairton Rd., Jefferson Hills, PA 15025Monongahela Volunteer Fire Department: 451 W. Main St., Monongahela, PA 15063Morris Township: 77 Park Dr., Prosperity, PA 15329North Franklin Township Fire Department: 565 Sylvan Dr., North Franklin Township, Washington, PA 15301North Strabane Fire Department: 2550 Washington Rd., Canonsburg, PA 15317Smith Township municipal building: 1848 Smith Twp. State Road, Slovan, PA 15078South Fayette Township Library: 515 Millers Run Rd., Morgan, PA 15064South Park Township Library: 2575 Brownsville Rd., South Park Township, PA 15129Upper St. Clair Community & Recreation Center: 1551 Mayview Rd., Upper St. Clair, PA 15241Washington Mall: 301 Oak Spring Rd., Washington, PA 15301Washington Park: 900 East Wheeling St., Washington, PA 15301