Reusing household water in a food garden: which water helps and which harms

South Africa's water shortages remain a worry for farmers, and with El Niño raising concern about dry conditions, urban growers who rely on municipal tap water may struggle to keep their gardens productive. Reusing household water can help, but experts warn it must be done carefully to protect plants, soil and the safety of the food.

Oneziwe Jackson, a Cape Town farmer and food technologist, collects the water she uses to wash vegetables and the clean water that runs while she waits for a tap or shower to warm up, and stores it in buckets and a drum for her container garden. "No expensive equipment, no complicated system, just a few changes to my daily habits," she said. Water used to wash vegetables may suit the garden if it has no soap in it, she said, but dishwashing water can carry detergents, grease and food scraps, and some laundry products contain chemicals and salts that harm plants and soil. "Saving water must never come at the expense of our health."

Nkosinathi Mbele, a permaculture practitioner in Bez Valley, Johannesburg, has fitted gutters to his house to catch rainwater. He suggests looking at how water runs across the land: roofs, driveways and roads can direct runoff to collection points, and swales and small ponds can hold it for drier months. Filters of gravel, sand and broken shells trap solids, and mulch cuts evaporation, limits erosion and keeps down weeds that compete for moisture.

Tshwane plant pathologist Sibongile Jiyane said rinse water from fruit and vegetables is generally the better choice, and bath water may also be reused, but dishwashing and laundry water need more caution. Sodium and boric acid can damage plants or soil when they build up with repeated use, so households should check the products they use. Signs of stress include yellowing leaves, brown edges, wilting, stunted growth and poor germination, and a white crust on the soil can point to salt, though these symptoms have other causes too.

Water with bleach, strong cleaners or sewage should not be used unless properly treated. Jiyane advises pouring suitable greywater on the soil around plants, away from leaves and the parts people eat, which matters most for leafy crops such as lettuce and spinach. "Plants may appear healthy while still being exposed to potentially harmful microorganisms," she said.

Source: Food for Mzansi