A week after the first reports of small worms or larvae being discovered in tap water in the South Korean city of Incheon, the problem has spread to towns and cities across the country and the prime minister has ordered an urgent investigation. Residents of nearly 600 households in Incheon, a coastal city to the west of Seoul, have complained of finding worms in their drinking water. City officials believe that insects may have laid eggs in water treatment facilities, with the larvae then making their way through the city’s pipes to emerge from taps. Those initial reports were quickly followed by similar complaints from residents of Seoul, the surrounding province of Gyeonggi and the city of Busan, in the far south-east of the country. On Monday, Chung Sye-kyun, the prime minister, issued emergency orders for all 484 water purification plants across the country to be inspected and for the ministry of the environment to take measures to assuage mounting public concern about the safety of tap water. “The environment ministry and local governments should join hands to swiftly conduct investigations and disclose all relevant information to help ease public unrest”, Mr Chung was quoted as saying. Water officials in Seoul collected a larva measuring nearly half-an-inch long from a home in the centre of the city, reporting that it was about the thickness of a human hair and still moving. Tests of tap water samples taken from throughout the apartment building were unable to find any further signs of larvae or other contaminants, city officials said, leaving experts unsure as to the source of the problem. It has been suggested that the larvae are from fruit flies or other small insects that are laying eggs in shower or kitchen drains, or in apartment blocks’ water tanks. Unhappy Koreans are taking photos of creatures they have found in their drinking water and are sharing them on social media sites - and recalling problems with Incheon’s water supplies last year that were traced back to poor maintenance of water treatment facilities and saw rust-red water pouring from their taps. City authorities in Incheon have warned local residents not to drink tap water and tanker vehicles are being dispatched to parts of the city that have been affected. Some 49 kindergartens and schools across the city have stopped providing meals to students and parents are being asked to provide their children with packed lunches. Convenience stores have reported that sales of bottled water are soaring, while new shower filters are also selling well.