1. Wastewater irrigation - hazard or lifeline? Gez Cornish & Neeltje Kielen HR Wallingford Ltd. UK

2. Wastewater irrigation - hazard or lifeline? Based on field studies in Nairobi and Kumasi The need for a typology of wastewater irrigation Variations in microbiological water quality Positive impacts of wastewater irrigation What are the trade-offs? The need for “interim” water quality standards Summary:

3. Wastewater irrigation - hazard or lifeline? The need for a typology of wastewater irrigation : Great variation exists in wastewater: sources conveyance systems treatment in-field management A typology is essential to guide discussion of practice or the formulation of guidelines or regulations.

4. Wastewater irrigation - hazard or lifeline? Source ConveyanceTreatmentDisposal Formal collection network Road tankers Natural drainageNone Natural / Biological Conventional Irrigation Groundwater recharge River or surface water body Industrial Municipal Informal Backyard Indirect use Direct use Indirect use A proposed typology Formal use = Use of wastewater with a certain level of permission and control by state agencies Informal use = Use of wastewater lacking permission and control by state agencies Direct use = Wastewater conveyed to a defined area for irrigation Indirect use = Wastewater discharged into water bodies with scattered and uncontrolled downstream abstraction Informal use Informal or formal use

5. Wastewater irrigation - hazard or lifeline? Examples - Mau Mau Bridge, Nairobi Informal, indirect. Untreated municipal waste. Natural drainage channels running to river. Surface & overhead irrigation of vegetable crops sold in local Nairobi markets.

6. Wastewater irrigation - hazard or lifeline? Examples - Maili Saba, Nairobi Informal, indirect. Untreated municipal waste diverted from sewer to fields. Surface irrigation of vegetable crops grown for home consumption and sold in local Nairobi markets.

7. Wastewater irrigation - hazard or lifeline? Examples - Asago, Kumasi Informal, indirect. Untreated municipal & industrial waste. Natural drainage to river + dumping by vault emptying tankers. Overhead irrigation of vegetable crops, grown mainly for Kumasi market.

8. Wastewater irrigation - hazard or lifeline? Variations in water quality - Nairobi

9. Wastewater irrigation - hazard or lifeline? Variations in water quality - Kumasi

10. Wastewater irrigation - hazard or lifeline? Positive impacts Area Study area irrigated (ha) No. of HHs (ha) Kumasi 502,700 12,70011,900 Nairobi 125,700 3,7002,220

11. Wastewater irrigation - hazard or lifeline? Positive impacts Main crops Av. Revenue US$ / ha Total value of production Nairobi Kumasi Kale, tomato, spinach, green maize, cabbage Tomato, garden egg, okra, chilli 1,770 (annual)544 (7 months) US$ 3.9 million US$ 6 million

12. Wastewater irrigation - hazard or lifeline? Positive impacts - revenue + profit, Nairobi Farmer Cost $US Revenue $US Profit $US Plot area ha 1 2 3 4 5 6 Overall 237 232 -40.109 417 1,802 1,3850.143 60 68 80.041 33 196 1620.088 1 63 620.032 0 60 600.069 124 403 2790.080

13. Wastewater irrigation - hazard or lifeline? Positive impacts - profits, Kumasi

14. Wastewater irrigation - hazard or lifeline? What are the trade-offs HH income Urban food supply Nutrient recycling Managed waste disposal Chronic ill-health Wide-scale disease outbreaks Damage to soils & groundwater CostsBenefits Where is the greatest ‘public good’ secured?

15. Wastewater irrigation - hazard or lifeline? Interim water quality standards Current WHO guidelines: Apply to TREATED wastewater Aim to secure “no measurable excess risk of infection” Use of UNTREATED wastewater is widespread. Under these conditions: “No risk” standard seems unrealistic A single threshold is unhelpful - all wastewater is not equal Are there acceptable levels of risk & what do they imply? Can we provide greater guidance - risk assessment scales? Can quantitative microbiological risk assessment models provide these answers?