A participant sips ordinary water from a cup, and is able to taste what a second participant is drinking.
Conditions in place throughout the effect include:
1. The participant can feel and sniff inside the cup, making sure nothing has been added.
2. You NEVER secretly drop anything into the water.
3. They can drink the water BEFORE and AFTER the taste changes.
4. Neither the cup, nor the water, is ever switched.
An alternative presentation is also taught, which will allow you to remove a person's ability to drink water. They take a sip of the water and it tastes normal. Yet the moment you suggest that they'll become "hypersensitive" to the chemicals in the water, they find that it tastes absolutely revolting! They will refuse to take another sip! But, when you finally convince them to take a drink, it tastes like regular water once again.