14.3.5 Chemical disinfection methods
There are several commercially available products designed for treating water at household level.
Chlorine solution, also known as sodium hypochlorite solution or bleach, is the most affordable, easiest to produce, and most widely available chemical for household water treatment. It is supplied in bottles and has easily interpretable instructions for use on the side of the bottle. Typically, the procedure is to add a capful of chlorine solution to a 25 litre water storage container, then shake and wait for 30 minutes chlorine contact time before drinking. Double dosing is advisable if the water is visibly dirty.
Contact time is the amount of time that elapses when two substances are mixed. Chlorine contact time means the time between the introduction of chlorine and using the water.
Aquatabs are a specifically formulated and branded solid form of sodium dichloroisocyanurate (NaDCC) (see Figure 14.6). NaDCC is stable in Aquatabs form as a solid which gives it a longer shelf life and makes storage, handling and transport much easier than with liquid bleach. One Aquatab contains 67 mg of NaDCC and treats 20 litres of clear water. For visibly turbid water, two tablets per 20 litres are needed. It is very important to mix well and leave for 30 minutes contact time before consumption.
‘PUR Purifier of Water’ is the brand name of a combined flocculant and disinfectant product produced by Procter and Gamble (Figure 14.7). It is now on the market in Ethiopia although it may not be widely available across the country. PUR can be used to treat raw source waters with a wide range of turbidity and pathogen load. This water treatment chemical allows flocculation to take place and helps to remove Giardia and Cryptosporidium cysts that are resistant to chlorine disinfection. (A cyst is a dormant stage in the life cycle of some protozoa and bacteria that is resistant to adverse environmental conditions and therefore difficult to destroy.) PUR comes in sachets with one sachet needed to treat 10 litres of water.
Flocculation is a process in which suspended solids are removed from water and turbidity is reduced. The solid particles lump together to form ‘flocs’ which slowly settle to the bottom of the container. A flocculant is a substance that can be added to water to encourage this process.
|Figure 14.6 Aquatabs tablets for household water treatment. (Photo: Abera Kumie)||Figure 14.7 PUR Purifier of Water. (Source: as Figure 14.2)|
Wuha Agar is a chlorine-based water treatment solution that is used in Ethiopia (Figure 14.8). The procedure is very similar to other chemical treatment methods. For a 20 litre jerrycan, add one capful of Wuha Agar, cover and shake. After 30 minutes contact time you can use it.
14.3.4 Solar disinfection