The UN say that a human being needs 50 litres of water per day in order to prepare meals and to have enough for personal hygiene. 50 litres of water per day are necessary in order to avoid diseases and to retain efficiency.
However, many humans in Africa must get along with 20 litres water per day. That is the quantity of water that we use when having a shower for 1,5 minutes.
In Germany, the water consumption per person amounts to 121 litres water per day. About 1/3 is for toilet-flushing, 1/3 for body hygiene, 1/3 for laundering, washing the dishes, cooking and drinking. For cooking and drinking, we need about 5 litres per day.