Urban Harvest

With over 12 years’ experience in organic food gardens across Cape Town, Urban Harvest shares some valuable lessons in water harvesting for the future.

By installing water harvesting solutions for clients and greywater systems at under-resourced schools, Urban Harvest has been learning some valuable lessons in organic food gardening. 

Urban Harvest blog images Feb1

Over the past 12 years, Urban Harvest has designed, installed and maintained 338 organic food gardens across the city of Cape Town and partnered with MySchool to install greywater systems. Anticipating a growing stress on gardens and people under drought conditions, here’s a guide to the four common sources of non- municipal water you can harvest:

1. Rainwater 

Rainwater harvested off your roof is suitable for irrigation and sanitation, but will need professional filtration to make sure it’s safe for drinking. The amount you can harvest is limited to your available roof space, storage and the amount of rain that falls.  

Bear in mind that even a very light, short rain can go a long way for you if you have clean gutters, enough storage and collection points. For example, just 6mm falling on a 400m2 home rooftop will harvest approximately 2200 litres of fresh water, whereas a school with 3000m2 of rooftop can harvest 10800 litres. 

To calculate how much you can harvest at your home /school or business, simply multiply the surface area of your roofs by the average rainfall for your area. While you may not know exactly how much rain will fall, it’ll give you a good guide to help you choose the right size of tank.

2. Greywater

Greywater collected from baths, sinks and washing machines is suitable for flushing toilets and watering ornamental gardens. Unfiltered grey water should be used as soon as possible and shouldn’t be stored for more than 24 hours to avoid ecoli and bad smells.  Unfiltered greywater is also not safe for use on vegetable gardens, which is why Urban Harvest’s systems incorporate constructed wetland filters which biologically clean the water before storing it and using it in the gardens.  Unfortunately if taps are turned off, there won’t be much grey water to harvest but even so, every drop counts so reusing whatever you have will be essential. 

3. Well points 

Well points draw on natural aquifers up to 9 meters deep. While relatively inexpensive to install, you’re not guaranteed of finding water. If you do, the flow may not be year round and will certainly become less reliable with increased consumption in your neighborhood.

If you do incorporate well point water into your holistic water harvesting approach, it’s essential to have it tested regularly. In most cases, it will only be good for toilets and gardens, but again, a good filtration system would vastly improve the quality. 

4. Boreholes 

Boreholes are expensive and are also being put under increasing governmental regulation. Installers are drilling deeper and deeper (up to 200 meters) to access the depleting, non-renewable precious resource of deep ground water.  As such, boreholes don’t necessarily offer a complete solution for water sovereignty. But, if they are used, they need to be used with moderation and respect and should form part of an integrated approach including serious rainwater harvesting and greywater recycling. 


Along with water harvesting, Urban Harvest MD Ben Getz explains it needs to be coupled with reduced water consumption and expectations: “Conventional toilets, for example, use a huge amount of water to flush while composting toilets use no water… So why are we treating clean drinking water like sewerage?”  He points out that even though change can take a while, it’s definitely worth starting today. 

Writer credentials: Ben Getz - Managing Director of Urban Harvest