We manage with wood, we'll manage with plastic.

Everything needs water, so it'll effectively always be about water management.

Also, if necessary we can add poison to the plastic just for those things that really need it (underground pipes mainly I suspect).

What the world really needs is a strong, light, cheap material that lasts, after water contact, at full strength, about 3 months, and degrades in a couple of years.

I've always wondered if there way a cheap way to engineer cellulose or lignin into a material like this. But it's gotta be really cheap.