December 2001
Good Afternoon
Drinking water from a water tank or off the roof
It would be true to say that with the very nature of our business
(that is, the designing and building 1900 replica homes) most of
our projects are built on rural land. Regardless of where people
build, almost every aspect of building is the same except for two
things, water and sewerage discharge.
In this country, far too often we take our water supply for granted.
We live in clean, green and unpolluted New Zealand; our water supply
must be good. Unfortunately the reality is often far from that.
I will say this, the water quality has improved greatly since the
first days of domestic water tanks.
You might say to yourself: "I would have thought that 80 to
100 years ago our water quality would have been far higher or less
contaminated", and I would have to agree with you, except for
one thing. And that is, all roof flashings, roof nails, spouting
and downpipe joints and joints in our galvanised corrugated iron
water storage tanks were made from lead. Actually it's only been
in about the last five years that galvanised and lead roof and water
systems have been replaced with zincalume, aluminium, rubbers and
plastics.
Not to mention all the paint we used on our roofs was lead-based,
no such thing as colour steel back then. Even in the city or urban
areas, huge amounts of plumbing materials and fittings were lead.
But it was the properties that had no town water supply that were
most at risk. I remember when I was a kid, we were living in a district
beyond the town water supply and had to rely on water collected
from the roof. I think all we had were two 800 gallon corrugated
galvanised steel water tanks for a family of five. They would need
continual repairs as the fittings around the outlets would always
leak, not to mention that occasionally the water would start to
smell from opossums or birds that had fallen in, couldn't get out
and drowned. It would be dad's job to fish them out. However, putting
it in perspective, that was 30 years ago and I have never suffered
from ill health neither have any of our family. Dad died two years
ago at 81, and mum is still going strong at 87.
These days we use plastic or concrete tanks with lead-free water-tight
connections and fittings, and are 99% vermin proof. The intakes
from the gutters all have grills and leaf catchers. However that
does not mean that the rain water we collect is uncontaminated,
just because we have eliminated the lead and dead animals, although
the quality is hugely improved. You'll still get bird droppings
and wind blown gunk landing on the roof only to be washed into your
water supply the next time it rains.
If you are concerned about your water quality there are two ways
to test it. Make inquiries at your regional council as to where
you can acquire sterile water testing bottles. In my case I got
them from the Wellington Regional Council district office in Masterton.
The tests are easy and the first tests for bacteria. Take your
sterile bottle to any tap in the house. Run the tap for 15 seconds
to ensure the water is water from the tank and not that which has
been sitting in the pipes. Take the full bottle down to your local
hospital or medical centre. There they have access to bio-lab testing
facilities. They will charge you for testing the water but it could
be a investment not a cost if people are getting sick and you're
not sure why.
In my case (taken about two years ago) the report came back to say
there was some bacteria in the water that should be treated. It
said that the occupants of the house would build up a resistance
to the bacteria and it probably wouldn't affect them. However if
we were having guests who were used to town supply water, they could
have a mild case of an upset stomach.
We decided the best and safest thing to do would be to install
a water steriliser between the water tank and the first house tap.
It's a simple system. The water passes through a small unit and
across a UV light killing off a further 90% of remaining bacteria.
The second water test is for minerals and chemicals. You only test
for minerals and chemicals if your water supply is either from an
underground or bore water system or an unknown water supply. The
test procedure is very similar except this time you take the water
sample to the Wellington Regonol Council, tests cost between $50
and $150. One of the main reasons for testing for the presence of
minerals is if there is too much iron in the water it will end up
leaving rust stains in the toilet or bath. Other minerals corrode
the copper in plumbing fittings. You could imagine what sort of
damage could occur if in a couple of years of moving into a new
home water was starting to cause damage behind the walls because
pipes and fittings were leaking.
Below is an article on drinking water from the roof, put out by
BRANZ in the Build magazine.
Drinking
Water from the Roof
by Joe ten Broeke
a BRANZ Senior Technical Adviser
In many rural areas where there is no town water supply,
water is collected from house roofs for household use, including
drinking water. Which materials are safe to use for the roof
and storage tank? Which are not?
One of the New Zealand Building Code (NZBC) Clause G12 'Water
Supplies' is to safeguard people from illness caused by contaminated
water. Water supplies intended for human consumption, food
preparation, utensil washing or oral hygiene must be "potable",
i.e. safe to drink.
Will water collected from any roof be safe and potable? The
answer is NO! Some roof cladding materials are unsuitable
for the collection of drinking water. Others are only suitable
after some weathering, or after they have been washed by two
or three good rainfalls.
So what is suitable, what is safe and which materials require
washing before they are suitable?
What is not safe?
Water should not be collected from roofs built with the following
materials, since the water could be contaminated by dangerous
soluble substances from the materials:
· lead, commonly in the form of lead flashings (especially
if unpainted)
· lead-based paints
· asbestos-cement products]
· CCA-treated wood shingles-
· LOSP-treated wood shingles
· bituminous materials.
What needs washing?
The following materials require rain washing or weathering
before drinking water can be collected from them:
· new, untreated cedar shingles must be allowed to
weather first, since this timber is naturally acidic
· newly applied acrylic roof paint needs one or two
good rain showers first, since detergent foaming can occur
when it is new
· fibre-cement products (not containing asbestos) are
safe, but they also require at least two good periods of rain
washing to remove potentially harmful particles.
What is suitable?
Water can be collected from the following roofing materials
(from new) without any risk, as long as they are clean:
· galvanised steel roofing
· zinc/aluminium-coated steel roofing
· clay tiles
· factory-painted steel
· factory-painted tiles
· zinc materials
· stainless steel
· butyl (but note that black butyl rubber will release
material as it weathers)
· mineral-fibre asphalt
· slate
If the materials you want to use are not listed here, ask
the manufacturer for written information about the suitability
of their products for water supply collection.
Indirect contamination
Beware of contamination from run-off from upper storey wall
claddings landing on a lower level roof that is used to collect
drinking water. In particular, avoid run-off from uncoated
CCA- or LOSP- treated timber cladding such as plywood. Remember
that timber stain coatings also may contain harmful fungicides.
Always disconnect the storage tank before roof cleaning, Any
cleaning substances used to remove lichen or moss from roofing,
such as chip-coated tiles or clay tiles, must not be allowed
into the tank. Thorough washing may be required after roofing
has been treated with such substances.
Water storage tanks
Galvanised steel tanks were traditionally used for storage.
Sizes varied and tanks were usually placed as high as possible
so that gravity could supply the required pressure. Larger
tanks were either built on or into the ground, of concrete
cast insitu, or pre-fabricated ferro-cement. A pump was then
used to supply the water to the house. In recent times, polythene
tanks have become widely used. Tanks with volumes of 20,000
litres are available
Remember that run-off from a zinc/aluminium-coated steel roof
will corrode galvanised steel.. With such roofs, use a polythene
storage tank and PVC spouting and downpipes. Not that the
manufacturers of zinc/aluminium-coated steel cladding, materials
state that they are not suitable for water tanks.
Regular checks
Rainwater is safe to drink. But when water is contaminated
by airborne dust, pollen, leaves and bird droppings on the
roof, the quality of the collected water can become degraded
and made unhealthy. Therefore, it is important to regularly
check water quality, clean out spoutings, and properly maintain
any filter systems and/or chemical treatment systems.
|
If you would like further information please contact us at the Moss
Brothers Housing office.
Kind regards & season greetings
Julian Moss
|
