In much of the developed world, chlorine often is added as a disinfectant to tap water. If the water contains organic matter, this may produce other byproducts in the water such as trihalomethanes and haloacetic acids, which has shown to increase the risk of cancer. The level of residual chlorine found at around 0.0002 g per litre, which is too small to cause any health problems directly. The chlorine concentration recommended by World Health Organization is between 0.0005 and 0.0002 g/L.