Household water treatment systems
Practical Action
Nitrites and nitrates have been associated with methaemoglobinaemia; this is when a larger
proportion of haemoglobin is caused to turn into methaemoglobin which means less oxygen is
able to be carried in the blood. This leads to cyanosis, especially in bottle-fed infants of 3-6
months old, and is also known as ‘blue baby syndrome’. Nitrates can leach into groundwater due
to the use of fertilisers or from wastewater. It is better to prevent the intrusion of nitrite and
nitrates into the water source since it is difficult to treat. The removal of nitrates is covered in
Nitrate Removal Storage: A Review of Possible Mechanisms and a Summary of Observed
Changes by the Water Research Association.
Fluoride is present in all natural water but high levels can lead to mottling of teeth and skeletal
fluorosis. Coagulation and activated alumina can remove excess fluoride. Activated alumina is an
adsorbent; a highly porous material made from aluminium hydroxide. Activated alumina may be
available and affordable for communities in developing countries (WHO, 2004). To find out more
about fluoride removal, IGRAC have published Fluoride in Groundwater: Overview and evaluation
of removal methods.
Arsenic also occurs naturally depending on the type of rock the water filters through. High levels
of arsenic can lead to skin lesions and higher risk of cancer. Arsenic contamination and its
removal are covered in a separate document; see A Small-scale Arsenic and Iron Removal Plant.
Biological Contaminants
Faecal-borne pathogens can be transmitted by water but it must be remembered that these
diseases can also be passed through any faecal-oral route.
Parasitic worms, like roundworms, flatworms and guinea worms can transmit their eggs to
humans through drinking water and cause infection. They must be completely absent from any
water supply.
Legionella bacteria are common in hot and warm water pipes. Infection happens through
inhalation of mist or spray. It causes Legionnaires’ disease which can lead to pneumonia
associated with respiratory function.
Cyanobacteria, also known as blue-green algae, produce dangerous toxins called cyanotoxins.
Cyanotoxins can affect humans in various ways depending on the type of toxin and on whether it
has been ingested or has contact with skin.
For more detail on the various types of infection that can be transmitted by water, refer to the
WHO (World Health Organisation) website and the book Environmental Health Engineering in the
Tropics.
Physical Contaminants
These include particles and suspended solids. This is mostly a problem when sourcing surface
water and varies seasonally due to heavy rains and velocity of the water flows. Drinking turbid
water is dangerous; solids in water can provide the perfect environment for bacteria to breed.
Suspended solids must always be removed before disinfection.
Turbidity is measured in NTU (nephlometric turbidity units) using a turbidity tube. If water is
more than 5 NTU then turbidity must be reduced before disinfection. A sedimentation test must
be carried out to obtain settling times for the suspended solids and decide on whether a
coagulant is needed in order to remove colloidal matter. Colloidal matter appears as a fine
suspension and will take longest to settle because particles are statically charged, making them
more attracted to water molecules. For more on sedimentation and coagulation see
Sedimentation.
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