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Space Station Freedom (SSF) will be operational for up to 30 years with missions lasting up to 180 days. Because of the need for large amounts of potable and hygiene water for the crews, it will not be practical to supply water from the ground (as was done for Skylab) or to generate water from fuel cells (as is done for the Shuttle). Hence, waste and metabolic waters will be reclaimed and recycled in SSF. Because of the unique nature of the water sources and the closed loop recycling processes, providing safe water will be a challenging task. Developing a program for the verification of SSF water quality to ensure crew health is the responsibility of NASA's Medical Sciences Division at the Johnson Space Center (JSC). This program is being implemented through the Environmental Health System (EHS). This paper will describe the strategy for the development of water quality criteria and standards, and the associated monitoring requirements.

Potable water for the Shuttle orbiter is generated as a by-product of electricity production by the fuel cells. Water from the fuel cells flows through a Microbial Check Valve (MCV), which releases biocidal iodine into the water before it enters one of four storage tanks. Potable water is dispensed on-orbit at the rehydration unit of the galley. Due to crew health concerns, iodine removal hardware is installed in the chilled water inlet line to the galley to remove the iodine from the potable water before it is consumed by the crew. The Shuttle water system is sampled to ensure water quality is maintained during all operational phases from the disinfection of the ground servicing equipment through the completion of each mission. This paper describes and summarizes the Shuttle water quality requirements, the servicing of the Shuttle water system, the collection and analysis of Shuttle water samples, and the results of the analyses.

Microbial proliferation in the STS potable water system is prevented by maintaining a 2-5 ppm iodine residual. The iodine is added to fuel cell water by an iodinated ion exchange resin in the Microbial Check Valve (MCV). Crew comments indicated excessive iodine in the potable water. To better define the problem, a method of in-flight iodine analysis was developed. Inflight analysis during STS-30 and STS-28 indicated iodine residuals were generally in the 9-13 ppm range. It was determined that the high iodine residual was caused by MCV influent temperatures in excess of 120 °F. This is well above the MCV operating range of 65-90 °F. The solution to this problem was to develop a resin suitable for the higher temperatures. Since 8 months were required to formulate a MCV resin suitable for the higher temperatures, a temporary solution was necessary. Two additional MCV's were installed on the chilled and ambient water lines leading into the galley to remove the excess iodine.

To satisfy a requirement to supply water to Mir station, a process for treating iodinated water on the Shuttle was developed and implemented. The treatment system consists of packed columns for removing iodine and a syringe-based injection system for adding ionic silver, the biocide used in Mir water. Technical and potable grade water is produced and transferred in batches using collapsible 44-liter contingency water containers (CWCs). Silver is added to the water via injection of a solution from preloaded syringes. Minerals are also added to water destined for drinking. During the previous four Shuttle-Mir docking missions a total of 2781 liters (735 gallons) of water produced by the Shuttle fuel cells was processed using this method and transferred to Mir. To verify the quality of the processed water, samples were collected during flight and returned for chemical analysis.

On the International Space Station (ISS), humidity condensate will be collected from the atmosphere and treated by multifiltration to produce potable water for use by the crews. Ground-based development tests have demonstrated that multifiltration beds filled with a series of ion-exchange resins and activated carbons can remove many inorganic and organic contaminants effectively from wastewaters. As a precursor to the use of this technology on the ISS, a demonstration of multifiltration treatment under microgravity conditions was undertaken. On the Space Shuttle, humidity condensate from cabin air is recovered in the atmosphere revitalization system, then stored and periodically vented to space vacuum. A Shuttle Condensate Adsorption Device (SCAD) containing sorbent materials similar to those planned for use on the ISS was developed and flown on STS-68 as a continuation of DSO 317, which was flown initially on STS-45 and STS-47.

Controlling microbial growth and biofilm formation in spacecraft water-distribution systems is necessary to protect the health of the crew. Methods to decontaminate the water system in flight may be needed to support long-term missions. We evaluated the ability of iodine and ozone to kill attached bacteria and remove biofilms formed on stainless steel coupons. The biofilms were developed by placing the coupons in a manifold attached to the effluent line of a simulated spacecraft water-distribution system. After biofilms were established, the coupons were removed and placed in a treatment manifold in a separate water treatment system where they were exposed to the chemical treatments for various periods. Disinfection efficiency over time was measured by counting the bacteria that could be recovered from the coupons using a sonication and plate count technique. Scanning electron microscopy was also used to determine whether the treatments actually removed the biofilm.

The ability of iodine to maintain microbial water quality in a simulated spacecraft water system is being studied. An iodine level of about 2.0 mg/L is maintained by passing ultrapure influent water through an iodinated ion exchange resin. Six liters are withdrawn daily and the chemical and microbial quality of the water is monitored regularly. Stainless steel coupons used to monitor biofilm formation are being analyzed by culture methods, epifluorescence microscopy, and scanning electron microscopy. Results from the first two years of operation show a single episode of high bacterial colony counts in the iodinated system. This growth was apparently controlled by replacing the iodinated ion exchange resin. Scanning electron microscopy indicates that the iodine has limited but not completely eliminated the formation of biofilm during the first two years of operation.

Two simulated spacecraft water systems are being used to evaluate the effectiveness of iodine for controlling microbial contamination within such systems. An iodine concentration of about 2.0 mg/L is maintained in one system by passing ultrapure water through an iodinated ion exchange resin. Stainless steel coupons with electropolished and mechanically-polished sides are being used to monitor biofilm formation. Results after three years of operation show a single episode of significant bacterial growth in the iodinated system when the iodine level dropped to 1.9 mg/L. This growth was apparently controlled by replacing the iodinated ion exchange resin, thereby increasing the iodine level. The second batch of resin has remained effective in controlling microbial growth down to an iodine level of 1.0 mg/L. Scanning electron microscopy indicates that the iodine has impeded but may have not completely eliminated the formation of biofilm.

The ability of iodine to control microbial contamination and biofilm formation in spacecraft water distribution systems is being studied. Two stainless steel water subsystems are being used. One subsystem has an iodine level of 2.5 mg/L maintained by an iodinated ion-exchange resin. The other subsystem has no iodine added. Stainless steel coupons are being removed from each system to monitor biofilm formation. Results from the first six months of operation indicate that 2.5 mg/L of iodine has limited the number of viable bacteria that can be recovered from the iodinated subsystem. Epifluorescence microscopy of the coupons taken from this subsystem, however, indicates some evidence of microbial colonization after 15 weeks of operation. Numerous bacteria have been continually recovered from both the water samples and the coupons taken from the noniodinated subsystem after only 3 weeks of operation.

The development of a spectrophotometric analyzer for use on water samples in microgravity environments is discussed. The instrument is constructed around a commercial spectrophotometer, the Hewlett-Packard HP8453, with a separate turbidimetric analyzer, here a modified Hach 2100P ratio turbidimeter. Flow-through sample cells were constructed for each instrument to support microgravity use and sample deaeration. Spectrophotometric analyses on aqueous samples on orbit are sensitive to the presence of undissolved gases in the samples. In a micro-g environment, free gas in samples can and does remain suspended, clouding the mixture and interfering with spectral optical density measurements. This paper discusses the design of a spectrophotometric analyzer, with particular emphasis on the merits of two approaches to eliminating free gas interferences in on-orbit water analyses: hyperbaric gas redissolution and deaeration across a hydrophobic membrane.