Why would you choose to live somewhere with no clean water, for 30 years?
Incredibly low rent, or no rent at all in an otherwise unaffordable location to live (the South Island).
Although you could own the physical structure that is a house on a First Nations reserve, you can never own the land.
Because of this, most of the home mortgages on a First Nations Reserve are held by the Band through special CMHC programs, and the occupant (who has to be First Nations) pays a very low rent. All of this is heavily subsidized by the Federal Gov't.
Often, a Band Member will pay no rent or mortgage on a family home ... and the land is provided by the Federal Government through the Indian Act.
So in other words, rather than pay $2500.00 a month for a three bedroom, you can live with dirty water coming out of your taps essentially for free. If your income is low, or non-existent, you literally become obliged to remain living where you're currently living ... dirty water or not.
So he likely couldn't afford to move anywhere else, especially if his housing costs were next to nothing in terms of what it would otherwise cost to live around here.
Even if he could afford to live elsewhere, a combination of family ties, social connections, the Indian Act, and the fact that First Nations reserves are, by design, the historical and heredity lands of the occupying First Nations citizens ... often make the concept of moving elsewhere untenable, or impossible.
That inability to own the land your home sits on means you can never build any equity in your home and property, and you can never make your own infrastructure improvements (a situation that's a direct result of the Indian Act), and is also a foundational element of many of the issues (like clean water) that First Nations deal with.
The take-away though, is that not providing fresh drinking water to a First Nations reserve, when water is available, plentiful and clean, and when providing that water is your legal obligation (the Federal Gov't through the Indian Act), is utterly unacceptable, and in the case of providing First Nation Canadians with clean drinking water in 2022, completely inhuman.