Sunday, March 17, 2013

Overseas community service (OCS)/ Youth expedition project (YEP) part 2: How do I know if that water is safe?

For those working in developing countries:
In case you are still not sold on the idea of drinking from rainwater based on my previous post (Overseas community service (OCS)/ Youth expedition project (YEP) part 1: Is that water safe?), read on. Incidentally, some communities do not want to drink rainwater because of tradition and culture. They have drinking from surface water (ponds, rivers, lakes) since the time they were born, they do not see other sources of water as viable. Depending on the situation, you may not want to fight an uphill battle to suddently switch their drinking habits to a rainwater source. Perhaps, you may be better off convincing them of implementing some treatment method.

I have been consulted by organisations which want to operate in developing countries and know more about the safety of their drinking water. An approach similar to the one below may be used.

1. Geography
If you are collecting surface water, know what is upstream. (This was covered in the previous OCS/YEP post but I will add some more information here.) Residences, villages, resorts, tourist attractions or heaven forbid, industries and agriculture upstream should light up a big red flag with a buzzing alarm... Drink the raw water at your own BIG risk.

But knowing the land use should extend to more than just along the waterways. Know your watershed! (In Singapore, we call it catchment basin or drainage area instead.) Your watershed is basically the land area acting as a big umbrella to catch and convey the rain to your water point. It includes the forests, parks, carparks, roads, other built up areas for the rain to flow over before reaching your water collection point. Naturally, any substance (e.g. litter, oil, animal droppings, soil, minerals) on the ground surface is fair game for the rainwater to pick up as it flows to your water point.

So you say that your river does not flow past any industry but if your watershed has a leather tannery or beer brewery, their waste chemicals may find their way into your river (and your mouth if you are drinking from the river).

Traditionally, we use topographical maps to delineate the watershed. In simple terms, water always flows from high to low points. Join up all the high points surrounding your water collection point and you have set the boundaries for the funnel into which water flows. (You may refer to Georgia Adopt-a-stream file here for a better description of the process. In fact, I strongly recommend that website as it contains a lot of useful information for water quality monitoring.)

However in current times, computer software and GIS (geographical information system) are used to calculate the watershed.

Of course, you may not have a topographical map. (Some countries consider this a state secret. Even in Singapore, it is not easy to get one.) Much less the digital map for your area of interest. Then the next best method will be to check out the areas adjacent to the waterway upstream of your water point. An area 1-2 km from your waterway will be a good start. Same as before, check out the landuse patterns in these areas. Does anything stick out like a sore thumb?

Figure: Sample topographical map. Useful to delineate your watershed if you don't get overwhelmed by the amount of details in the map. It also tells you quite a bit on the landuse in your watershed.

Figure: Students' rendition (sketch) of the landuse patterns around Ngee Ann Stream

To be continued...

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