It is better to play the game outside near a water tap or in a bathroom.
Give participants two water cans and tell them that they have 5 minutes to put one of the jugs on the scale with exactly 4 gallons of water in it.
Obviously we can't fill the 3-liters can with 4 liters of water." So you need to get the 4 liters into the 5-liters can.
Fill the 5-liter can all the way. Pour water into the 3-liter can until it is full. Now you have 2 liters in the 5-liter can and a full 3 liters in the 3-liter can. Empty the 3-liter can. Pour the 2 liters of water still in the 5-liter can into the 3-liter can. Now the 3-liter can has 2 liters of water in it, and more importantly, 1 liter of empty space. Fill up the 5-liter can all the way, and then pour water out of the 5-liter can into the 3-liter can until the 3-liter can is full. This leaves exactly 4 liters in the 5-liter can.
After the activity you can debrief about probelem solving technics emphasizing the fact that solution is always hidden inside the probelem.
One water can (3 liters)