> Would {bIQ SeHjan yIchu'}/{bIQ SeHjan yIchu'Ha'} be fine?
I think that would get the point across. Whether or not it's what Klingons "actually say" is of course difficult to know, but I'd say that's fine until canon proves otherwise.
Another option might be to focus on the water pipe, i.e. {qatlhDa' yIpoSmoH/yISoQmoH.}, or on the water itself, as in {bIQ yIghItmoH/yIghItHa'moH.}.
> How would you say "the water is cut"?
I think you could use the verb {peS} or {Qay}, along with whatever negative construction might be appropriate to the situation: {bIQ QayHa'lu'.}, {bIQ peSlu'Qo'.}, {bIQ Qaylu' net bot.}, etc.
If the water isn't running and you're not sure why, you could hedge your bets with {narghbe' bIQ.} or {ghItbe' bIQ.}.
//loghaD