Household water treatment systems
Practical Action
Roofwater Harvesting
Although there are fewer of contamination for roofwater, care must be taken to take into account
contamination from the roof, gutters, piping system and storage facility. Water from rooftops
should be filtered and boiled before consumption.
There is no risk from iron sheeting itself (usually a layer of oxidisation forms on the galvanized
sheet), but there is a risk of bacteriological contamination if there are animal faeces on the roof -
from birds, lizards, etc. A roof should be kept as clean as possible and a first flush system used
to wash away the first couple of millimetres of rain during the first storm of the season.
There is evidence that using asbestos sheeting can be used without risk, as it is only through
inhalation (and not through ingestion) that asbestos is harmful (WHO, 2003). The World Health
Organisation concluded there is no evidence that asbestos in drinking water is carcinogenic and
therefore would not publish a guideline for asbestos levels in drinking water.
Most grasses are not suitable; only certain types of hardy grasses are suitable for rain collection
on thatch.
The use of lead pipes and fittings (especially if water is acidic) can result in high levels of lead in
the water and can cause neurological damage.
See the technical brief Rainwater Harvesting.
Water Treatment Methods
The World Health Organisation (WHO) ranks the treatment processes available according to their
technical complexity in Table 1, the higher ranking being more complex. It is usually the case
that the more complex the system, the higher the capital and operating costs.
Table 1: Ranking of technical complexity and cost of water (WHO, 2008)
Ranking
Examples of Treatment Processes
1 Simple Chlorination
Plain filtration (rapid sand, slow sand)
2 Pre-chlorination plus filtration
Aeration
3 Chemical coagulation
Process optimisation for control of DBPs
4 Granular activated carbon (GAC) treatment
Iron exchange
5 Ozonation
6 Advanced oxidation process
Membrane treatment
In order to ensure water is acceptably free from both sediments and pathogens, a multi-stage
treatment is best to consider. This document will outline several processes which should be
considered as different stages of the cleaning process. Choosing which processes to adopt will
depend on the quality of the water being treated, what contaminants need to be removed, the
scale of operations and capital and operating costs. Costs to bear in mind would include, but are
not limited to, local labour, mechanical and construction works, chemicals, electricity and life
expectancy.
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