I have written previously about foreign bodies in bottled water and occasional misuse of 19 litre bottles. I was amazed to find out that the bottles are often used in chemistry experiments in schools to demonstrate dangerous reactions between various substances and water.
The picture, taken from a chemistry journal, shows the violent reaction resulting from the addition of metallic sodium to water. You may remember this demonstration from your school days. While I understand that this is a safer option than an open dish, it is not setting a good example. Do not try this in the bottling plant!