If you are actually thirsty, you are WAY past due for some water...so don't wait til you're thirsty to drink. If you are drinking water and have nice clear pee and never really feel thirsty....I would say don't even worry about it.
I would be extremely cautious about replacing water with juice...because sugar is really, really not good for your body and is especially "not awesome" during pregnancy. The way that our bodies break down sugars and the chemical process that takes place once it is broken down is not good for your body if you are taking in more sugar than your body needs..and honestly, we don't need much. The kinds of sugar that are packed into everything we eat these days are especially bad for us. ACTUAL sugar is nowhere near as bad as some of these sugar substitutes we eat so much of these days.
But things like coconut milk are awesome if you want something "more" than water...raw milk, etc. Just watch out for things like "minute maid" and other brand name juices...which are essentially trash food which give you very little if ANY of the benefits printed on the label and do more harm than good, really.
I've been sucking royally at staying hydrated this pregnancy. I'm letting myself get WAY too thirsty before I drink and it's driving me nuts. I've just been so crazy busy and running around this time! I've been very distracted. I drink very little in the first part of the day....and then a ton in the latter part of the day when I get a headache and remember to drink...the days are just passing so quickly!!!