Water shortages, aggravated by climate change, are likely to increase in the future. Significant savings in drinking-quality water could be made if recycled water was used for household laundry.

A recent study suggests that recycled water is safe to use in domestic washing machines and is not a health hazard. In Australia, where the study was conducted, about 15 per cent of domestic water is used for laundry purposes. In some areas, 'dual reticulation' schemes deliver both high quality drinking water and lower-quality recycled water to households via separate pipes.

The researchers investigated the degree to which pathogens (or microorganisms which could cause disease) could be transferred from recycled water to hands, sample fabrics, nearby surfaces and the air during a typical household laundry cycle. They concluded that only extremely low quantities of bacteria and viruses are likely to transfer from the recycled water to people or surfaces and that these are unlikely to pose a health hazard.

Using a series of cold-water washes with no laundry products, researchers examined the transfer rates of four types of pathogens: Eschericha coli (a bacteria that infects the intestines), MS-2 and PRD-1 bacteriophages (types of viruses used experimentally in place of harmful viruses that infect the intestines) and Cryptosporidium parvum egg cysts (used experimentally in place of tiny pathogens that infect the intestines). The researchers investigated four routes for the pathogens to 'escape' from the recycled water:

1. Recycled water to fabrics. Between just 0.001 per cent and 0.09 per cent of the pathogens were transferred in this way. The level of transfer of C. parvum cysts and E. coli to all fabric types was greater than for MS-2 and PRD-1, possibly because they are larger and stick more easily to fabrics. In addition, more microorganisms attached to cotton towelling than other fabric samples (poly-cotton knit and cotton knit). This could be due to the greater absorbency and rougher surface structure of the towelling fabric. These results suggest the degree to which bacteria attach to fabrics depends on both the type and properties of the bacteria, and the physical and chemical properties of the fabric.

2. Recycled water directly to hands. Overall the transfer rate from water to hands was about 100 to 1,000 times less than the amount transferred from water to fabric samples. The greatest transfer rate between water and hands was for E. coli and the least for MS-2.

3. Fabric samples to hands. The study estimated less than 12 per cent of the seeded E. coli in the fabric was transferred from fabric to hands. Less than 0.1 per cent of PRD- 1 was transferred from fabric to hands. Less than 0.19 per cent MS-2 was transferred in this way.

4. Recycled water directly to surrounding surfaces.

Contamination of surfaces through splashing or evaporation of the water was found to be 100 times less than the transfer rate from water directly to hands. Although the study suggests there is minimal risk to users of recycled water, consumers are also concerned about the appearance of water; for example, its clarity and colour.

The researchers suggest this study can support regulations to supply recycled water and to reassure the public that the use of high quality recycled water for domestic laundry purposes is safe.

Source: O'Toole, J. Sinclair, M. and Leder, K. (2009). Transfer Rates of Enteric Microorganisms in Recycled water during Machine Clothes Washing. Applied and Environmental Microbiology. 75(5): 1256-1263. Contact: joanne.o'toole@med.monash.edu.au��