The drawing above shows 500 litres of water as 250 people drinking for a day: each icon represents what one person drinks in a day (2 litres). It is roughly what you drink in nine months.
In other units, 500 litres is 0.5 cubic metres or about 132 US gallons. Change the number in the tool or pick another reference for the drawing (glasses, bathtubs, tanker trucks, Olympic pools…) with the "Show" selector.