The public is invited to see the City of Washington’s drinking water treatment plant. Last June the city’s reverse osmosis system to treat drinking water went on line. The reverse osmosis, or RO, system filters the water and makes it safe for the residents of Washington. The estimated project cost for the improvements to city water was $5.5 million. The open house is Thursday from 5 to 7 p.m. at 522 North 4th Avenue.