The drawing above shows 1,000 litres of water as 500 people drinking for a day: each icon represents what one person drinks in a day (2 litres). It is roughly what you drink in a year and a half.
In other units, 1,000 litres is 1.0 cubic metres or about 264 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.