Typically, a radiator leaking water results from the process of rusting or corrosion within the radiator leading to tiny holes forming on its surface. In the early stages, only a small level of discoloured water will drip from the rad, so it is not usually an emergency from the outset.
That said, you should tend to a radiator leaking water as quickly as possible to prevent the situation escalating and stop any further issues. For more detailed help and advice in dealing with a radiator leaking water, explore our blog on How To Fix A Leaky Radiator.