I think that, too, we have to keep KISS in mind - Keep It Simple, Stupid.
Remember where these islands were, and what the time period was. Getting a few bags of cement to one of these isolated islands was one thing, but hauling in enough construction materials and machinery to build a "proper" water well, or proper anything for that matter, wasn't going to happen. It was not the British way. It was "make do with what you have" as opposed to the American way, "overwhelming mechanized assistance." In the grand scheme of things, if NZ had decided to build an airfield on Niku, you can bet that a ship loaded to the gunwales with construction supplies and equipment would have appeared off the western reef in short order, much as happened at Wake Island right before the war.
Niku's colonization was a satellite operation designed to disperse natives from overtaxed islands to hopefully more fertile fields beyond. Even the Brits eventually realized that you can only do something with nothing for so long before the effort collapses under its own weight.
LTM,
Monty Fowler, TIGHAR No. 2189 ECSP