Dear Master Peter,

For some arrangement requires a glass of water, can I use a plastic cup instead of a glass? 

Can the cup or glass be opaque or must it be a transparent one?

For some arrangements , it can only be used for 3 months . What if we forget to remove for after 3 months ? 

Thank you.
 

Any cup, plastic or glass is fine. Both opaque or transparent is okay. Preferably, light blue or white color.

If your forget, it will have reverse effect.

Cheers.