WALNUT (CBSLA) — An environmentally conscious grade-schooler and her parents are trying to figure out the motivation behind a disturbing discovery inside her water bottle.

Payton Nova is one of the only only people in her class at Stanley G. Oswalt Elementary School in Walnut who uses a reusable water bottle, which is why she might be the only one who had something other than water in the bottle.

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“I took a little sip of it, and it was really salty, so I looked inside of my water bottle, and it was yellow,” the 11-year-old told CBS2 News.

She said there were a couple of other times her water didn’t taste right, but in this case, she showed it to her parents. They quickly deduced it was urine.

“I smelled it, and it was — urine is very specific,” said Payton’s mother Lulu Yen.

Payton’s parents took her to a doctor to make she was OK, then contacted the school and the Los Angeles County Sheriff’s Dept.

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At first, her parents thought it might’ve been a prank by one of the kids in Payton’s school. However, they now believe an adult might be behind the disgusting act.

“But I thought about it, and I thought. ‘That’s not the case,’ because if it was a practical joke, it’s usually meant for you to find out about it, and people sit together and laugh,” said Yen.

According to Payton’s teacher, the classroom is locked when students are away, which adds to their suspicion the culprit is an adult.

They said the only way to put their minds at ease is to push for a full investigation.

“We just don’t want it to happen to anybody else, and really, truly just understand why it even happened, because it’s so odd and so malicious,” said Yen.

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Payton’s parents said she will now only drink from clear water bottles, which aren’t as good for the environment, but at least she can see what’s inside.