According to the UN, the world is facing a severe water crisis at the beginning of the 21st century as a result of poor water resource management. Effective management requires participation from all populations, not just governments. One way individuals can help is by using a glass ball in their toilet tank, which occupies 250ml of space and saves 250ml of water per flush. If even 0.01% of the world's population used one, it could save over 2 billion liters of water per year at a cost of less than $1 per unit.