Joint post from HatamSoferet and MarGavriel
Part 1 – MarGavriel writes:
When Moses sends messengers to the King of Edom, requesting passage for the Israelites through his land, their message includes the following line:

May we please pass through thy land? we will not pass through fields or vineyards, and we will not drink water from the wells. (Numbers 20:17)

The Palestinian family of Targumim (“Targum Yerushalmi”), however, understands this figuratively:

May we please pass through thy land? we will not we will not bonk betrothed babes, nor will we violate virgins, nor will we make merry with married matrons.

And the paytan Yannai renders the verse thus, in his liturgy for the relevant Sabbath:

[Hebrew cut because Jewschool’s Hebrew seems to be on strike again. If you want to read the Hebrew you can go here.] We shall surely keep away from the field, and stay far from the vineyard,
Won’t seduce virgins, nor rape betrothed women;
We shall surely not taste from the waters of the well –
The married women, who are compared to the waters of a well.

Part 2 – HatamSoferet asks:How does that play out when Moses says in verse 19 “and if we drink from the wells, we’ll pay for it”? “We might accidentally have sex with your women, but if we do, we’ll totally pay you for them”?
Part 3 – MarGavriel responds: I’ll have to find a less fragmentary version of a Palestinian Targum, and see how it translates verse 19.
Then MarGavriel went to the library, and came back with the following:
All the Targumim seem to translate verse 19 literally.
So, why the first part, verse 17, nonliterally, and the second one, verse 19, literally?
We find an answer of sorts in the works of one Yochanan Eisenberg, in (Warsaw, 1900). He, like us, wants to know – where on earth did that come from? He’s working with the Targum of Jonathan:

Why did Moses ask the same question twice? The general claim about verse 19 [see, e.g., Rashi] is that Moses’s offer to the king of Edom said that the Israelites would refrain from drinking from the Miraculous Well [which travelled the wilderness along with Israelites], and buy water from the Edomites, so as to give them business – but the King of Edom did not agree. If this interpretation is correct, then why did he ask a second time, saying “and if we drink your water, we will pay”? The Jonathan is responding to this question.
Moreover, it is problematic that the text uses different expressions in verses 17 and 19. The first time, it says “water of the well”, and the second time, it says “your water;” the first time, it says: “we will walk on the King’s Road”, and the second time, “we shall ascend on the highway.” Moreover, why does verse 17 say that “Moses” asked him, and verse 19 say “the Israelites” asked him? And why did they say, the second time, “I and my flock”? And the expression “I shall pass through with my feet” is odd. And the word “to him” in verse 18 is redundant. And why did the King of Edom say the first time “You may not pass through me”, and the second time just “You may not pass through”, without saying “through me”? Finally, it is odd that he says: “Lest I greet you with the sword” — why lest? after all, if they trespass his land without his permission, he is definitely going to greet them with the sword.

These, in case you’re not used to the style, are the sorts of questions a certain kind of commentator concerns himself with. There is a sort of theological principle that no words in the Torah are superfluous; therefore, variations such as those cited must have meaning.
Another sort of commentator will look at the text and say “Huh, that’s oddly repetitious. Must be two narratives being merged by the redactor.” This is an interesting, but much less fruitful, kind of approach. We are taking the fruitful approach here, trying to find some meaning in the variations within the text.
Back to Eisenberg. He’s finished outlining the difficulties he sees with the text, to which he thinks the Targum is responding, and now he’s going to explain how the Targum’s non-intuitive translation answers all those difficulties.

The Jonathan had a deep intent with all this. Namely,
Moses wanted to uproot from the heart of the King of Edom any concerns that Israel would perform the activity which he himself was accustomed to do, and which was an inheritance from his ancestor Esau: “He used to hunt men’s wives and sexually afflict them” (Bereshit Rabba 61) – and as R. Jochanan says in Bava Bathra 16: “[Esau] slept with a betrothed maiden.” Therefore, [Moses] sent a message to [the King of Edom] which could be interpreted on two levels.
Now, there is nothing which hurts one’s fellow more than telling him the truth. Therefore, the King of Edom became furious at Moses. This is why verse 18 says “the King of Edom said to him,” where the word “to him” seems redundant. What it means is that his wrath was directed specifically at Moses, who had made a clever double entendre at him; it was not befitting the honour of a king to hear such language. And then, the second time, he was forced to greet him with the sword, on account of this.
This is why he said lo ta’avor an expression meaning evra (wrath), [thus meaning “don’t be wrathy at me!”]. And it also explains why he said bi, specifically at me – for I am the king. As it says in Proverbs 20: “The fear of a king is as the roaring of a lion: whoso provoketh him to anger sinneth against his own soul.” And because he had raged at Moses, the Israelites [and not Moses] needed to speak to him the second time. They needed to use language which was unambiguous, and eliminate any reference to the double entendre. This is why the language is different in verse 19. And the king’s response to that was simply lo ta’avor, “you may not pass through”, without the word bi.

MarGavriel finds this frightfully clever, but utterly unconvincing as an explanation of the targum, saying “Eisenberg is making his own ‘medrash,’ as it were.” (This, by the way, is what I mean by “fruitful.”)
On reflection, I’m inclined to take a lesson from an exchange I heard in the Yeshivat Hadar kitchen between an Israeli and an American. They were arguing over the proportions of water and soap to use when doing dishes. The American, used to thinking of water as an unlimited resource, used little soap and much water. The Israeli, used to thinking of water as a valuable and expensive resource, used little water and comparatively much soap.
How’s that work? Well, if you’re used to thinking of water as plentiful, you are inclined to look at the exchange between Moses and the King of Edom and think “What’s all the fuss? It’s only water. They’re even going to pay for it.” But what is as ubiquitous as, yet more valued than, water? Women. This Targum Yerushalmi suggests to me, at any rate, that for the King of Edom, water is as guarded a commodity as women. Perhaps he is reluctant to let a horde of Israelites drink up his limited water supplies. Just as you can’t offer to pay him for his women, so too you can’t offer to pay him for his water.
Not as elegant a solution, perhaps.