As Nick Stauner's explained in his answer, both "take the word" was used to refer to "to accept their word for a conclusion of the issue." However, it might be beneficial to consider each of the involved sentences, one at a time. Here is the first one.
People want to use it to cook with and they're looking to take the word.
This is obviously related to the question "But how do you convince people that the water supply is, in fact, safe?". It means people want to use the water, and they want to be assured that the "water is safe".
We can understand this take the word by looking up the words take and word in a dictionary. For example, here are the related entries from Macmillan Dictionary,
take 5 [transitive] to accept something that someone offers you
word 4 [singular/uncountable] news or information about someone or something
Thus, we can understand "they're looking to take the word" as the people are looking to accept the news or information (in this case, the approval from the Health Department, according to a preceding paragraph in the transcript). Also note that this is not a common usage, as J.R. and others commented. Take someone's word for it is more idiomatic and recommended for learners.
Here is the second sentence,
And I believe if they say to go ahead, I would take their word for it and I think the public, at large, will, too.
The phrase take someone's word for it is common enough that dictionaries would list it. Here is what I found in the same dictionary,
take 5a. to accept an explanation or something that someone says without discussing it or arguing about it
take someone's word for it (=believe what someone tells you): You don't have to take my word for it – ask anyone.
This means that the mayor trust the Health Department, and if they say the water is safe, he would believe them.
No worries or no problem both work perfectly here. The issue with a one-word response is that brevity over text can easily be interpreted as being annoyed or otherwise upset with the person you're talking to.
There are a number of ways you can soften a short okay to convey the proper meaning, however. This is less the realm of proper, conventional English, and more the realm of complicated text etiquette. Essentially, you need to add something that conveys the appropriate tone. "Okay!" is perfectly acceptable, and "Okay :)" may be seen as a bit informal, due to the smiley face, in business settings, but is not entirely unheard of.
Unfortunately, there is no one word in English that will easily convey everything you want to put into this text. If your goal is ultimate clarity, something like
No worries, take your time
is still quite a bit more than one word, but will leave little room for misinterpretation.
Best Answer
Someone can either leave or take a leave, but they are fundamentally different in meaning.
leave alone means "go away from a place" (or, figuratively, from a person).
Leave in take a leave is short for "leave of absence", aka a break or holiday from work.
So no option in your use case.
Unfortunately, most varieties of
although technically correct may come across as somewhat rude for native speakers. But getting the message across without breaking the unwritten rules of hospitality is a dilemma even native speakers face. I recommend looking towards Miss Manners & co. for advice: