POTENTIAL HEALTH RISKS FROM GREY WATER

David Cunliffe

What is Grey Water ?

Shower and bath water 33 % of total wastewater generated

Hand basins5 %

Laundry23 %

Kitchen7 %

Total - about 70 % of wastewater is grey water

Purpose of Grey Water

Sanitation and cleaning

Washing hands, skin, clothes, food etc to remove pathogenic microorganisms, oil, grease and dirt

- higher loads from washing clothes/nappies from babies and young children

Aim is to separate people from harmful microorganisms by carrying them away in grey water.

Other uses

Washing animals, cleaning tools, transporting urine, disposal of hazardous waste (chemical)

What is in Grey WaterBathroomPathogenic microorganisms (Thermotol coliforms <10-106 per 100 mL), hair, skin, soaps, oil, grease (Sewage ~ 106-1010 thermotol coliforms per 100 mL)

LaundryPathogenic microorganisms (Thermotol coliforms <10-107 per 100 mL), bleach, soap powders (boron, sodium, phosphate, ammonia, surfactants), lint

KitchenPathogenic microorganisms (Thermotol coliforms <10-106 per 100 mL), detergents, food particles and residues, oils, fats, hazardous wastes

Unknowns

Washing of nappies and other faecally-soiled clothing

Washing of pets

Disposal of hazardous liquids

Washing of tools

Health Risk

Depends on hazards present in the source water and exposure (+ mosquitoes)

Exposure controlled by managing:

- method of application - public accessibility- use

Risk Source

Lower Laundry rinse

Laundry wash and rinse

Bathroom

Higher Kitchen

Other risk factors - young children and pets

Heath risk by source

Risk Method

Lower Sub surface

Drip

Spray

Higher Hose

Other risks - ponding/storage can support mosquitobreeding

Heath risk by application method

Risk Method

Lower Trees and shrubs

Lawn

Fruit trees

Vegetables

Higher In house (toilet flushing)

Other risks - non-approved cross-connections

Heath risk by use

Risk Accessibility

Lower No access

No access by young children

Higher Unlimited access

Heath risk by accessibility

Conclusions

Grey water usually contains fewer hazards than sewage but concentrations vary over a very wide range

For on-site systems the concentration and range of hazards will depend on household management

Restricting methods of application and types of use can reduce risk but for on-site systems this will rely on household management

Systems need to be robust and designed to involve a minimum of maintenance. Centralised management systems are best.