A liter of water weighs 1 kilogram. A kilogram converts to 2.2 pounds, so a liter of water weighs 2.2 pounds. This assumes that the weighing takes place at sea level and the water is at 4 degrees centigrade (39.2 degrees Fahrenheit).
Because the temperature of water alters the density, it therefore alters weight as well. This happens for both increases and decreases in temperature. At 93.3 degrees Centigrade (200 degrees Fahrenheit), the liter of water would weigh 2.12 pounds, 0.08 pounds lighter. Additionally, as the altitude increases, the gravitational effect decreases, and so does the weight. The altitude affects the weight by an almost negligible amount, but the mass remains constant.