[The Following is an excerpt from a letter to Allen Meece]

[Updated 5 September 2002]

The "black" wastewater system consists of three identical baffled tanks that serve as waste traps for the galley sink, hab bath water dispenser (shower and sink), and the toilet. The water in each waste trap tank is treated with ammonium chloride and stored there until the tank can be removed or vacuumed out and its contents carried by hand to the hab bath's toilet, which is equipped to serve as a waste boiler. Since the chemical toilet and sink traps both use the same water treatment chemical and are the same size, the water in the sink traps, having few particulates, can be used in the toilet for double duty before final disposal in the boiler. The boiler vents through the cabin wall. The shower trap tank is shown positioned underneath the bath floor, but is actually accessible through the bath water dispenser.

The "gray" wastewater system consists of a non-removable water tank in the bath water dispenser to collect water from the cabin dehumidifier and store it for washing. It provides gravity-fed cold water to the shower. Because it provides water at a lower pressure than the drinking water system, it can also be topped off from the hot water line for later use.

The shower, power system, and toilet are the extent of water reclamation in this scenario. It is less mass intensive to haul up more water than it is to employ more thorough water treatment.

The water lines are small to keep flow rates small. The drinking water system is pressurized to flow up above deck without pumping, but not at high pressure. This saves tank & pipe mass, conserves water by reducing the flow rate, makes refilling easier and reduces the consequences of tank leaks into the cabin's sealed environment. Lower flow rates allow use of on-demand water heating by small in-line heaters, which conserves power. The compressor is the only vital electric component required to supply drinking water to the crew.

Drinking water is treated with small amounts of iodine instead of chlorine, the latter being more likely to accumulate in the cabin, and aerated by the tank compressor. Iodine need be added so infrequently that the injector can be operated by hand during refills. Water from the power system is recycled for drinking, requiring a reverse osmosis filter (not shown) for the power system to remove the iodine, and a small pump to flush it. This will ultimately poison the RO filter over several months, but the pump circulation returns most of the iodine to the water supply. Iodine will ultimately degrade a reversible fuel cell as well, but an RO filter will extend its life considerably. 10kW fuel cells can be built with modular design, and have capacity to spare.

The water system should also be relatively compact. There are only two water dispensers in my entire hab floorplan, separated from each other by just 1.5m. And the power system should snuggle up on the tanks as well.

Here are two sketches, to scale, of the water tank, antifreeze tank and fuel cells relative to the hab bath & galley. The floor is omitted, as is one wall of the hab bath (which has its own flooring). A single vertical section of the hab truss is included for perspective. The galley is omitted in the first picture for a better view.

Because it would freeze outside, the entire water dispensing system is located inside the cabin. The fuel cells are included for the same reason. The antifreeze tank is placed inside because that's where the heat is. The row of water tanks and fuel cells shown are just under 6 meters in length -- most of the crew cabin's length. Together, they provide most of the interior thermal mass of the hab and much of its heat as well. There is still some space below the hab flooring for heat exchangers, tankage and other uses, provided what's stored there doesn't mind the warmth.