It is not my field, but if plentiful and accessible, we are talking about several thousand tonnes of water around an small habitat that could theoretically be used. Nevertheless, if I understood right, that immense amount of water would have a limited shelf life until acidification corrodes the containment structures, so it would need to be continuously treated and refrigerated (It could not be used for human consumption neither),

" Ionizing cosmic radiation is mostly gamma rays and protons, which are overall very similar to the radiation from nuclear waste. Protons are slightly lighter and so would have less energy at a given velocity (more easily stopped); but, because they're protons, if captured by the water they'd basically become H+ ions which could acidify the shielding water in time (not seen as much with nuclear waste). " [1]

[1] https://space.stackexchange.com/questions/1336/what-thicknes...

Chemically neutralizing the shielding water should be trivial. But why would the water need to be refrigerated? Energy absorbed from radiation would be emitted as thermal radiation, and lose a ton of thermal energy during the long lunar nights. If well insulated, the water tanks could serve as thermal batteries to keep the rest of the base warm.

I said it for to maintain undesired chemical reactions under control. My first thought after to read some papers would be below 25°C, but this is not my field so take it with a grain of salt, as the water temperature in normal operating conditions within nuclear waste water pools seems to be held below 50°C by the refrigeration systems.

In any case, personally, I would not stay in a place like that with current shielding technologies even if I were paid for it.

PS. I'm not sure if it would be trivial treating the water for to keeping it operative more than one year as effective shield.

I did a few rounds with an AI on this topic, so excuse me if there are inaccuracies, but:

- According to a study conducted NASA, a 1 mm layer of polyethylene reduces solar and cosmic radiation by approximately 50%

- A 1mm, 1m^2 layer of polyethylene weighs approximately 0.92kg

Maybe the polyethylene would decay, but maybe it can also be remanufactured, harvesting the contaminates in the meanwhile?

That said, this all implies that working under a polyethylene sheet of 5mm would reduce exposure to about 33 mSv a year (assume 8hrs a day working on surface, 260 days/yr).

That said, Maybe robots can work on the surface instead?

Any notion of the rate of that acidification? I can't imagine its happening quickly, still very fun to think about