In rural areas each property may be served by a soakaway system, which can be described crudely as a rubble filled hole in the ground which the water permeates away from into the surrounding water table.
However, in older properties, traditionally, it may have been 'combined' with the foul waste water in one sewer, which means it flows to the Treatment Works (WwTW) and undergoes the same costly and wasteful cleaning process.
Another problem with this system is the pollution that occurs when there is a heavy rain storm. Excess water entering the system has to be discharged through purposefully made overflows, and this spill to local watercourses, rivers or directly to the sea. The water utility companies have been pressured for many years and a massive investment has been made to eradicate this problem.
If your house is in a modern development it may drain to a 'storage' tank or pond where the outflow is hydraulically controlled to prevent increased risk of flooding. This is becoming more common due to the EA flooding regulations and a recent development is the use of Sustainable Drainage Systems or SUDS, to minimise the impact of further development on our overloaded river systems and flood plains.