Water Safety Plan
Guide
Roof Water Sources
Version 1, Ref S1.2
January 2014
Citation: Ministry of Health. 2014. Water Safety Plan Guide: Roof
Water Sources, Version 1, ref s1.2. Wellington: Ministry of Health.
Published in January 2014
by the Ministry of Health
PO Box 5013, Wellington, New Zealand
ISBN: 978-0-478-42702-8 (print)
ISBN: 978-0-478-42703-5 (online)
Previously published in 2001 as Public Health Risk Management
Plan Guide: Roof Water Sources, Version 1, ref s1.2. This
publication’s title and any reference within the text to ‘public health
risk management plan’ was changed in January 2014 to reflect the
December 2013 legislation change of the term ‘public health risk
management plan’ to ‘water safety plan’. No other changes have
been made to this document.
This document is available at: www.health.govt.nz
This work is licensed under the Creative Commons Attribution 4.0 International
licence. In essence, you are free to: share ie, copy and redistribute the material in any medium or
format; adapt ie, remix, transform and build upon the material. You must give appropriate credit,
provide a link to the licence and indicate if changes were made.
Contents
Introduction
1
Risk Summary
2
Risk Information Table
3
Contingency Plans
8
Water Safety Plan Performance Assessment
Ref S1.2
Version 1, January 2014
Water Safety Plan Guide:
Roof Water Sources
10
iii
Introduction
Rainwater is used as raw water by supplies with roof catchment systems. This Guide is
concerned with the collection of rainwater from the roof, its transfer to storage and its storage.
If an event occurs with a roof catchment (ie, contaminants get into the rainwater during
collection or storage), the following could happen:

If animal or bird excrement, or air-borne chemical contamination, is carried onto the
roof or guttering, germs or the chemicals can cause sickness

If material is dissolved from the roof, flashings, guttering or downpipes, heavy metals
can cause sickness (rainwater is corrosive)

If animal or bird excrement or chemicals get into the storage tank, germs or chemicals
can cause sickness

If volcanic ash falls on the roof, chemical contaminants can cause sickness

If the supply of water runs out, poor hygiene can cause sickness.
The maintenance of a roof catchment can present risks to health. These are acknowledged,
but are not discussed further as such risks are the subject of health and safety in employment
legislation.
The roof catchment and storage, and the risks associated with them, cannot be viewed in
isolation. The quality of the water reaching the consumer could also be influenced by the
following, if they are used:

filtration, which can remove particles and some types of germs (see the P6 series Guide
for the filter used in your supply)

disinfection, which will kill some types of germs (see the P7 series Guide for the
disinfection method used in your supply).
To make the document more self-contained for small water suppliers, this Guide includes
information about water storage. Guide D1 discusses storage more fully and may help in
understanding risks associated with storage.
Ref S1.2
Version 1, January 2014
Water Safety Plan Guide:
Roof Water Sources
1
Risk Summary
The event creating the greatest risk involved in operating a roof catchment is animal or bird
excrement, or chemical contaminants, getting onto the roof (see S1.2.1).
The most important preventive measures are:

keep the roof and guttering clear of overhanging branches (S1.2.1.1)

regularly inspect and clean the roof and guttering (S1.2.1.1–2)

disinfect the water (S1.2.1.1–2).
(References in parentheses are to the Risk Information Table.)
2
Water Safety Plan Guide:
Roof Water Sources
Ref S1.2
Version 1, January 2014
Risk Information Table
Reliable information about water quality is essential for the proper management of a water
supply. Knowledgeable and skilled staff are also essential for minimising the public health
risks associated with water supplies. Please read the staff training (Guide G1) and the
monitoring guides (Guide G2). While we haven’t pointed out every detail of how these
documents are linked with the present document, the links are many and are important.
Abbreviations: DWSNZ – Drinking-Water Standards for New Zealand; MAV – Maximum acceptable value – see
DWSNZ:2000; council – regional/district council or unitary authority.
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: EXCREMENT AND CHEMICAL CONTAMINANTS CARRIED ONTO ROOF OR INTO GUTTERING
Possible hazards: Germs; herbicides, pesticides, other chemical contaminants that may be airborne.
Level of risk: High1
S1.2.1.1

Tree surgery.
Overgrown trees

Clean out guttering.
 May cause
bird life,
possums or
rotting
vegetation to
contaminate
the roof
catchment
area.


Provide a grate over

the downpipe-gutter
connection, or over
the whole guttering,
to limit entry of

vegetation into the
tank.
Check tree
growth at least
annually.


Check guttering

at least
annually.
Overgrown
trees.

Tree surgery.

Disinfect water in
tank or treat with
UV at point of
use.

Disconnect
downpipe from
tank and clean
guttering.

Disinfect water in
tank (1 mg/L of
chlorine for clean
water,* possibly
up to 5 mg/L if
water is poor
quality) or treat
with UV at point of
use.
Dirty guttering.
E. coli is
detected in
100 ml sample.
Microbiological
quality directly
after rain.
 Water dripping
off branches
onto the roof
may carry
contaminants.
 Dead animals
may fall into
the guttering.
S1.2.1.2

Faecal
contamination
from birds or
animals on roof or 
in guttering.

Keep roof and
guttering clean and
use first flush
diverter.
String wire along
the ridgeline to stop
birds roosting.
Take actions to
avoid attracting
birds, such as not
feeding them and
ensuring that
rubbish disposal is
secure.

Microbiological
quality.

Quarterly
inspection of
roof and
guttering for
faecal
contamination.

Faecal
contamination
on roof or in
guttering.

Disconnect
downpipe from
tank and clean
roof and guttering.

E. coli is
detected in
100 ml sample.

Disinfect water in
tank (1 mg/L of
chlorine for clean
water,* possibly
up to 5 mg/L if
water is poor
quality) or treat
with UV at point of
use.
*
About 1 teaspoon per 2L bucket.
1
It is primarily the microbiological hazards introduced into the water by this event, rather than the chemical, that
give it a high level of risk. However, overspraying events will create a high risk due to chemical determinands.
Ref S1.2
Version 1, January 2014
Water Safety Plan Guide:
Roof Water Sources
3
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: EXCREMENT AND CHEMICAL CONTAMINANTS CARRIED ONTO ROOF OR INTO GUTTERING
cont’d

S1.2.1.3
Record incidents of
roof contamination
from the air, and
seek assistance
from the council to
reduce these
(discharge
consents).


Consider using an
alternative source
(less affected by
aerial discharges).


Use first-flush
diverter or
disconnect
downpipe, before
first rain after
possible
contamination
episode.
Industrial,
agricultural or
domestic
discharges to air
(including aerial
spraying) settle
out on roof.
S1.2.1.4

Ensure your
chimney stack is
long enough that
material from the
fire will not settle on
the roof.

Ensure that the

contractor is aware
that the roof is used
to collect drinking
water, and that
overspraying must
be avoided.
Contamination of
roof and guttering
during spraying to
protect roof
timbers against
borer and other
insects, or

proofing against
spiders.

2
4
Obtain a guarantee
from the contractor
that persistent
organochlorine
pesticides will not
be used.
Use first-flush
diverted or
disconnect
downpipe, before
first rain after
treatment of the
roof.
Sample for
possible
contaminants
from all nearby
emissions –
seek advice on
likely
contaminants.
Obtain details of
all nearby
agrichemical
applications.
Nature of
pesticides used
by contractors.

Water contains 
contaminants at
concentrations
more than 50%
of their MAV.

Noticeable taste
in the water.

Algal growths if
fertilisers have
contaminated
the roof.

Visible deposits
of ash/soot on
the roof.
Seek action from
the council to
reduce
discharges to air if
from a small
number of
sources.

Make use of a
new source
unaffected by
discharges to air
(eg,
groundwater).

Locate alternative
source.

Install a first-flush
diverter.

Lengthen
chimney.

Phenols or lead
in water.

Clean acid glaze
from slow-burning
fire smoke off
chimney.

Use of
persistent
organochlorine
insecticides by
contractor.

Use different
contractor.

Decontaminate
the roof.

Use alternative
supply until
decontamination
is complete.
Pesticides in
water following
treatment of

roof timbers, if
there is concern
about the

nature of the
pesticides used,
and the way in
which they were
used.
Knowledge of
overspraying
events.
Water contains
pesticides at
concentrations
more than 50%
of their MAV.2
The risk associated with this event will depend on location within the country.
Water Safety Plan Guide:
Roof Water Sources
Ref S1.2
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: EXCREMENT AND CHEMICAL CONTAMINANTS CARRIED ONTO ROOF OR INTO GUTTERING
cont’d
S1.2.1.5

Ensure access to
the roof is made as
difficult as possible,
by removing such
things as ladders.

Inspect the roof
regularly for
deliberately
introduced
contaminant
sources (eg, bags
of chemicals).
Vandalism/
sabotage.

Check the roof
for unexpected
objects on it,
and the area
surrounding the
building for
objects that
may make
access to the
roof easier.

Evidence of
unauthorised
access having
been gained to
the roof.

Eliminate means
by which access
to the roof was
gained.

Remove
contaminant
source,
disconnect
downpipe and
wash down.
Event: MATERIALS DISSOLVED FROM THE ROOF, FLASHING GUTTERING AND DOWNPIPES BY THE
RAINWATER
Possible hazards: Heavy metals (lead, copper, chromium, cadmium).
Level of risk: Moderate
S1.2.2.1
Lead-containing
materials (paint,
nails or flashing)
used in roof
construction;
guttering
constructed from
corrodible
material (eg,
copper).

Use lead-free
materials on the
roof (paints,
flashings, nails).

Inspect
condition of the
roof surface at
least annually.

Keep roof surface
well maintained.


Use plastic
guttering.
Test for heavy
metals in roof
paint (one-off
test probably
sufficient).
Ref S1.2
Version 1, January 2014

Heavy metals in
the water if
there is a likely
source of them
on the roof.

Roof surface in
poor condition
and needs
repainting or
replacing.

Replace
inappropriate
materials.

Repaint roof, or
replace roof.

Leaded paint

test on roof
paint is positive.

Heavy metal
concentrations
in the water are
more than 50%
of their MAV.

Cases of lead
(or other heavy
metal)
poisoning, but
be aware that
such cases may
have other
causes.
Replace guttering.
Water Safety Plan Guide:
Roof Water Sources
5
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: CONTAMINATION OF THE WATER WHILE IN THE STORAGE TANK
Possible hazards: Germs; plasticisers (di (2-ethylhexyl) phthalate), possible reduced disinfection efficacy by
chlorine because of high pH.
Level of risk: High
S1.2.3.1
Animal or human
access to storage
tank (see
S1.2.3.5).

Ensure the storage
is covered.

Install mesh on

vents, overflow, etc.

Undertake regular
tank inspections
(monthly).


Monthly tank
inspection.
Microbiological
quality.

E. coli is
detected in
100 ml sample.

Dead animals
found in tank.

Mesh/grills
disturbed by
animals to get
access.
For wooden tanks:
– install metal band
around wooden
tanks to prevent
animal access
from ground level

Unpleasant
taste and odour.

Water turbid.

E. coli is
detected in
100 ml sample.

Dead animals
found in tank.

Mesh/grills
disturbed by
animals to get
access.

Unpleasant
taste and odour.

Water turbid.

Disinfect tank
(1 mg/L of
chlorine for clean
water, possibly up
to 5 mg/L if water
is poor quality)
depending on
water quality.

Replace or
provide mesh
where necessary.

Prepare tank
inspection
schedule.

Instigate
inspection and
cleaning
programme.

Install a second
tank.

Reduce tank size
for faster
turnaround of
water.
– remove
vegetation near
tanks
– install internal
liner for tank roof.

S1.2.3.2
Accumulation of
sediment in tank.


S1.2.3.3
Water stagnant in
plastic tank for too
long.
S1.2.3.4
Ensure the material
chosen for the tank
is suitable for
drinking-water
purposes.

Locate tank in a
shaded area.

Position inlet into
the tank near the
bottom to ensure
good mixing and
avoid stagnant
zones near the tank
bottom.

Dissolution of lime 
from new
concrete tank
(this problem
should reduce as
the tank ages).
6
Undertake regular

(annual) cleaning of
tank.

Use two storage
tanks, the first
feeding into the
second, and draw
water from the
second (this
reduces sediment
being carried
through into the
reticulation).
Line the tank.
Increase buffering
capacity of the
water (eg, addition
of sodium
bicarbonate).
Water Safety Plan Guide:
Roof Water Sources
Monthly tank
inspection.
Microbiological
quality.

Taste.

Plastic taste.

Sample for
phthalates
(plasticisers).

Di (2-ethylhexyl)
phthalate
concentration is
more then 50% 
of its MAV2.

pH.

pH above the
guideline range
(7.0-8.5).
Flush tank a
number of times
on first filling.

Relocate tank to
area that is
cooler.

Relocate inlet to
tank.

Add sodium
bicarbonate until
pH reaches an
acceptable level.
Ref S1.2
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: CONTAMINATION OF THE WATER WHILE IN THE STORAGE TANK cont’d
S1.2.3.5

Vandalism/
sabotage.
Restrict access to
tanks (fences,
locked hatches).

Regular
inspection of
tanks for
evidence of
unauthorised
access.

Evidence of
unauthorised
access having
been gained to
the tank.

Fence tank, or
provide lockable
hatches.
Conductivity.

Chemical
contaminants
still present at
concentrations
greater than
50% of their
MAV.


Conductivity of
the water is
5–10 mS/m
higher than
normal.
Repeat cleaning
procedure until
analytical results
for water
demonstrate that
contaminants are
present at
concentrations
less than 50% of
their MAV.

Tank and roof
not cleaned
sufficiently
following ash
fall to ensure
contaminants
are removed
from the water.

New tank.

New or additional
source.

Repair tank
and/or guttering.

Start water
conservation
measures.
Event: VOLCANIC ASH FALL ON ROOF2
Possible hazards: Arsenic, fluoride, and metals.
Level of risk: Low
S1.2.4.1

Volcanic eruption
results in ash fall
(pyroclastic fall).
Disconnect

downpipe into tank

as soon as possible
after eruption.

Use conductivity
test to determine
whether tank water
is fit to drink.

If tank water is not
fit to drink, empty
and clean out tank
when all ash falls
have ceased.

Clean roof,
guttering and
downpipe.
Fluoride,
arsenic, other
metals
suspected of
having elevated
concentrations.
Event: NOT ENOUGH WATER
Possible hazards: Hazards associated with poor hygiene.
Level of risk: High
S1.2.5.1

Lack of rainfall
combined with
insufficient
storage,
excessive use,
leak in tank, or
breach in
guttering.
2
Ensure tank size is
adequate. (Use
information about
annual rainfall
levels and number
of people using
supply to determine
size of tank
required.)

Ensure strength of
guttering is
adequate for wind
and snowfall
conditions.

Establish an
inspection
programme to
check guttering and
tank.

Conservation of
water.

Water level in
tank.

Water runs out
frequently.

Rate of water
use.

Water levels
low.

Regular
(monthly)
inspection of
tank and
guttering.

Evidence of
water leaking
from tank.
The risk associated with this event will depend on location within the country.
Ref S1.2
Version 1, January 2014
Water Safety Plan Guide:
Roof Water Sources
7
Contingency Plans
If an event happens despite preventive and corrective actions you have taken, you may need
to consult with the Medical Officer of Health to assess how serious a problem is.
Event – Roof contaminated by spraydrift or overspraying
Indicators:
Required
actions:
Responsibility:
8

Spraydrift or overspraying reported, noticeable taste or odour or
analytical results.

Reported illness in the community.

Identify sprayer and product used, and inform relevant
authorities, including MOH.

Drain contents of tank. Provide another source of potable water
until water of acceptable quality can again be supplied.

Disconnect down pipe from tank.

Clean roof and tank.

Confirm absence of chemical from water, by chemical testing,
after next rain.

Submit details to Driftnet (ESR).

Record details of incident.

Modify water safety plan (formerly known as a public health
risk management plan, PHRMP) if necessary.
Manager designated responsible for the water supply.
Water Safety Plan Guide:
Roof Water Sources
Ref S1.2
Version 1, January 2014
Event – Volcanic activity leading to ash fall on the roof
Indicators:
Required
actions:
Responsibility:

Media coverage of eruption.

Ash fall in area.

Normal range of conductivity values need to be known.

Disconnect down-pipe from tank.

Check quality of tank water through conductivity and pH tests.

If conductivity value is not elevated and pH is above 5, continue
use of tank water. If elevated (estimated increase of 5-10 mS/m)
or pH is depressed below 5, provide another source of potable
water until water of acceptable quality can again be supplied.

When ash fall is complete, clean roof surface, guttering and
down pipe, plus tank if necessary.

Conduct confirmation test of water to ensure that no elevated
concentrations of heavy metals are present.

Modify water safety plan if necessary.
Manager designated responsible for the water supply.
Event – Water shortage
Indicators:
Required
actions:
Responsibility:

No water, or tank level is low.

Increased levels of turbidity as water is drawn from lower levels
of tank.

Provide another source of potable water until water of acceptable
quality can again be supplied.

Identify the reason for the lack of water.

To avoid this happening regularly, install an additional or bigger
tank, or find a supplementary or new source.

Modify water safety plan if necessary.
Manager designated responsible for the water supply.
Ref S1.2
Version 1, January 2014
Water Safety Plan Guide:
Roof Water Sources
9
Water Safety Plan Performance
Assessment
To make sure that your supply’s water safety plan is working properly, periodic checks are
needed. The Overview document outlines what needs to be done. The following table
provides the detailed information for checking this particular supply element.
What to measure
or observe:

Corrosion metals

E. coli.
Follow the protocols set out in DWSNZ:2000.
How often:

For the monitoring frequencies for corrosion metals and E. coli
measurements see DWSNZ:2000.
What to do with the
results:

Results need to be recorded to meet legislative requirements or to
allow water safety plan performance assessment. The WINZ
database is good for this.

The collected data need to be periodically reviewed to see
whether problems with this supply element are developing. This
should be done as frequently as the manager responsible
considers necessary to minimise risk to public health arising from
this supply element.

Should this review show any unusual incidents, indicate that
proper procedures are not being carried out, highlight poor
laboratory results or indicate that poor water quality is reaching
customers, then review the procedures for managing roof
catchments.

Evaluate the monitoring results, and any actions taken as the
result of having to implement a contingency plan, to see if the
water safety plan needs modification – eg, preventive measures
are up to date; the contingency plan steps are still adequate; and
changes to the catchment system are recognised in the plan.
Responsibility:
10
Manager designated responsible for the water supply.
Water Safety Plan Guide:
Roof Water Sources
Ref S1.2
Version 1, January 2014