Treatment

Process

Hazardous Events

L

C

S

Risk Rating

Potential Hazards (General)

Water Source

On-site septic tank systems

3

3

9

H

Ÿ Escherichia coli, Cryptosporidium and other infectious organisms

Ÿ Turbidity, dissolved solids, colour and other physical contaminants

Ÿ Pesticides, heavy metals, nitrates, iron and other chemical contaminants

Domestic waste dumping

2

2

4

M

Municipal sewage effluent

2

3

6

M

Graveyards

2

2

4

M

Industrial activities

2

3

6

M

Leaking pipelines

1

2

2

L

Pesticide use

1

3

3

L

Petroleum refineries

1

3

3

L

Highway, railway accidents and spills

1

2

2

L

Recreational activities

3

2

6

M

Natural events—flooding, droughts, etc.

2

2

4

M

Raw Water Storage

Corrosion of storage tank

2

2

4

M

Ÿ Iron contamination

Ÿ Turbidity, dissolved solids

Settled sediments

2

2

4

M

Algae growth

2

3

6

M

Sand and Carbon Filter

Corrosion of filter tanks

2

2

4

M

Ÿ Iron contamination

Ÿ Turbidity, algae, dissolved solids

Insufficient backwashing

2

3

6

M

Incorrect backwash procedure

2

3

6

M

Spent Sand and Carbon

2

3

6

M

Reverse

Osmosis

Inadequate or inappropriate quality of pre-treatment

2

3

6

M

Ÿ Membrane fouling

Ÿ pH levels above normal range.

Ÿ Conductivity above normal range.

Ÿ Cleaning chemical concentrations at a level of possible health concern.

Poor flushing of cleaning chemicals from the membrane module.

2

3

6

L

Treated Water Storage

Algae growth

2

3

6

M

Ÿ Biological contamination

Micro

Filters

Clogging of filters

1

3

3

L

Ÿ Turbidity, dissolved solids

Ÿ Biological contamination

Incorrect positioning of filter cartridge.

1

3

3

L

Contamination of filter housing when changing the cartridge

2

3

6

M

Algae growth around the filters

1

3

3

L

UV Steriliser

Faulty UV light

1

3

3

L

Ÿ Biological contamination