Effluents? Guess My Vocabulary isn't Good

I noticed this sign in Jerusalem near a decorative fountain.

It bothered me. I guess I'm stupid. I wasn't familiar with the word "effluents," though I could easily guess the meaning, the intention of the sign. The colors of the sign, red and white indicate dangers, and the rest of the words do, too. It is clear that the water in the fountain is polluted or poisoned. That's obvious.

Like way back when, during my days as an EFL English Teacher, here I was stuck like many students, understanding only some of the words in a text. We used to be told to tell our students to guess the missing/incomprensible/unknown word. The experts insisted that the technique helps, and I would insist that it only helps with a certain higher level of students. My lower level and remedial would misinterpret the messages/texts and come up with incorrect ideas. And the wordier the texts the harder it would be.

I took a course to help lower level students to understand reading comprehension passages, and the first step we taught them was to step back and look. That's why I I considered the colors here so important. They mean danger. And the word danger also appears in the text. The problem is that the word water doesn't, though hopefully someone weak in English would know what "drinking" means.

For me the message was clear:

Don't drink the water! Dangerous!

Could it be poisonous or polluted? I had to look up the mystery word out of curiosity.

effluent [ef-loo-uh nt]

adjective

1.

flowing out or forth.

noun

2.

something that flows out or forth; outflow;effluence.

3.

a stream flowing out of a lake, reservoir, etc.

4.

sewage that has been treated in a septic tank or sewage treatment plant.

5.

sewage or other liquid waste that is discharged into a body of water, etc.

and
noun

1.

liquid discharged as waste, as from an industrial plant or sewage works

2.

radioactive waste released from a nuclear power station

3.

a stream that flows out of another body of water