You can either have your water checked or

[Silverobama]

There’s a rule here for passengers who want to take the subway train if they have water (in any kind of container) with them. They either need to give the water to the security person to check to see if it’s safe or drink some of it.

My translation:

You can either have your water checked or drink a mouth before passing the security check.

Please help me to make it natural.

 

[emsr2d2]

There’s a rule here for that passengers who want to take water, in any kind of container, on the subway, train if they have water (in any kind of container) with them. they either need to either give the water to the a member of security person to check to see if it’s safe or drink some of it themselves [in front of a member of security].

My translation:

You can either have your water checked or drink a mouthful before passing the security check being allowed through security.

Please help me to make it natural.

See above.
How do the security personnel "check to see if it's safe"?

 

[Silverobama]

How do the security personnel "check to see if it's safe"?

They have a machine and they'll put the water on the machine and see if it's safe. If it's safe, the button on the machine will become green, otherwise it'll become red.

You can either have your water checked or drink a mouthful before being allowed through security.

If I don't want to use "mouthful", is it also natural to say:

You can either drink the water or have it checked before being allowed through security.

I think it sounds much better than the original one. Please enlighten me!

 

[Skrej]

Yes, I'd use 'drink'. 'Take a mouthful' is unnatural, plus technically one wouldn't have to swallow. I gather the idea is that if you're willing to swallow the liquid, it's presumably safe. I doubt that's as reliable a test as the chemical analysis by machine, but that's beyond the scope of the language question.

Your second version is good.