Water sensitive design includes the use of fit-for-purpose water, and harvesting and/or storing water from various sources. In South Africa particularly we should reduce our dependence on surface water bodies (aka, dams). This presents an opportunity, but it also introduces a great amount of risk, particularly if these sources are more decentralised than what we are used to.
Our drinking water is treated at central locations before it is piped to our homes (if we are lucky to have piped water). That means that one central location manages this risk for us, and can afford the costs of accredited scientific analysis.
When we start looking at alternative sources of water, the analysis (and other) costs are carried by far less people and the relative cost of managing that risk increases.
To manage this risk in the urban environment, and help individuals manage this risk there are three complementary options:
- Map the water sources to illustrate what the likely contaminants and sources of risks are at a high resolution (as high as per dwelling, or perhaps more practically, per neighbourhood)
- Develop cheaper ways of analysis that, if it does not provide a complete picture, helps with qualitative information and shows when more tests are needed. Combined with the map, certain tests can have priority in certain applications, for example iron in groundwater, and E.coli in so-called springs.
- Appropriate point of use treatment technologies and strategies.
What exists in terms of mapping water sources?
As far as we know, there is no visual map, but databases do exist:
The National Groundwater Archive (NGA
)- a database of the DWA’s monitoring locations plus any other borehole they have found through hydrocensus. Drillers are supposed to register boreholes drilled on the database, but they rarely do. It’s outdated, geographic accuracy is highly variable. People used to use it as a starting point for doing a hydrocensus but you very rarely actually find the locations. It’s more useful for understanding hydrogeological context of an area – there are drilling logs, water levels, water quality (mostly qualitative but some quantitative) etc. It does include springs.
The WARMS database
where people who use water above a certain minimum level (as specified by the General Authorisations) have to register their water use. The users have to fill in a form which is not very explicit as the data accuracy varies wildly – coordinates are often wrong, water use is sometimes per property and sometimes per borehole.
There are a bunch of groundwater maps available at 1:500 000 scale:
The hydrogeological map series is available in digital form, but we’re not sure where they originate from.
All of these are national level.
In Cape Town, the city has a database of people who have registered boreholes. They now also require people to apply for permission before sinking a new wellpoint/borehole. This dataset is not publicly available.
None of these, from what we can see, is on a map, and thus does not show any relationship with the quality of the water and its location.
Ultimately, however, this needs to be user driven, from the bottom-up, perhaps in addition to the registered information noted above. How can we do this?
What exists in terms of cheap, safe, user-friendly and robust tools for water quality analysis?
From what we’ve seen, not much.
There are different types of testing:
- Electronic: Using sensors or probes that can include online or sim-enabled remote probes that can sample/measure dissolved oxygen, pH, electrical conductivity, total disssolved solids, salinity and voltage (if it runs on battery/solar power)
- Biosensors: Using biology to give a qualitative or quantitative signal, including the miniSASS, microbial cell counts, enzyme based processes etc
- Chemistry kits: examples include aquarium kits, swimming pool tests
- Visual investigation: through photography or microscopy
What exists in terms of appropriate point of use water treatment technologies and strategies?
There is no single answer to this. The categories of treatment include:
- Chemical (e.g. chlorine or ozone, and precipitation of e.g. iron salts),
- Physical (filtration, including reverse osmosis, sand filtering)
- Biological, which further can be categorised as bacterial, algal, macrophytes (wetland plants). One way of looking at this is how well-designed koi ponds function.
Adequate treatment invariably involves a combination of these, and while treating water to potable, or drinking water quality, the technology is similar to treating dirty water to protect the environment (like what happens in sewage works or koi ponds)