Kala Pani is a traditional concept that forbids Hindus from leaving India's borders and entering Mleccha territories, on pain of being excluded from their caste. The ban begins, officialy, beyond the coasts of India and the western bank of the Indus River. So were Hindu merchants forbidden to travel to Ceylon and the Maldives, which are in the midst of the Indian Ocean, even though these territories technically belong to the Indo-Aryan civilization? How far north and east could they go in compliance with the Kala Pani? Could they cross the Himalayas and Naga Hills (India's obvious natural frontiers) to reach Tibet or Burma, for example, or not? If anyone can tell me more, or at least point me to books to read, that would be great.
There are no precise limits to this, or indeed to anything like this.
Historically, edicts about specific geographical regions like this are
never precise, for a few reasons.
First and foremost, in an age before perfect maps, people don't know what things look like. Borders are often set according to rivers that don't exist, or mountains that are nowhere near where people think. Or let's consider the question of the Himalayas: if the Himalayas are the border, is it the first "layer" of mountains? The second? The highest? If the highest, how do we know which are the highest? It's far very hard to include significant portions of the Tibetan Plateau within "the Himalayas".
Kala pani forbids leaving the shores of India; what about the great lagoons of Kerala? What about Sri Lanka, which legend holds was once connected to India by a land bridge (for the record, it almost certainly was)? What about fishermen who leave in the morning but return each evening? These points are considered on a case-by-case basis by local holy men, so that it's possible that a priest in Delhi might say that
kala pani forbids fishing, but one in a fishing village in Tamil Nadu is likely to have a different opinion. And indeed, Panikkar writes
The idea that the Hindus had some kind of a ceremonial objection to the sea, while perhaps true in respect of the people of North India, was never true in respect of the people of the South. Peninsular India was maritime in its traditions and this is borne out also by Chinese records. Fa Hien writing in A.D. 415 states in the ship which carried him from Ceylon to Sri Vijaya, there were two hundred merchants all of whom professed the brahminical religion.
As it happens, this taboo does not address leaving India by land, and in fact this seems not to have been a problem, as the British used Indian troops in Burma and had no problem marching them there (though they took care not to send soldiers by sea).
There's also the issue of practicality. very few rules or laws are immune to being set aside when it's important, or even just convenient. Properly speaking,
Kala pani should forbid all seafaring. But we obviously see Indian sea merchants. Rituals existed from very early to allow someone to be cleansed of leaving home, and some merchants made regular use of them. As with many taboos in India, the requirements lay more heavily on the priestly castes than the working castes.
We
know that there were large ports in places like Calicut and Khambat, and that there were sailors from these places. However, we also see that in Kerala, the local Brahmins had nothing to do with the sea, preferring to leave it to Christians, Muslims, and Jews when possible, or to
Mukkuvars, a sort of special sea-faring caste.
I recommend reading Panikkar's
India and the Indian Ocean, though it can be hard to find. It's also not, like, centered around the black water taboo, it just mentions it here and there in connection with historical Indian seafaring. I'm not super familiar with pre-European Indian history, but I did some snooping because this question interested me, and there doesn't seem to be a lot of scholarship on the specifics of this practice, only mentions of it in the context of sea-faring.
