"Chookie" wrote in message "0tterbot"
wrote:

had lots of water ourselves last year too - i'm convinced though (along
with
the natural sequencers etc) that rain is different to water from a hose.

I think it's sheer quantity. 20mm falling from the sky all over my back
yard
does a lot more than 20 mm on a tiny area -- assuming I can actually get
20mm "rainfall" from my weeper hose.

The difference between rain and water from the hose is that rain has
nitrogen in it. Dunno where I first read this but I read it years ago.

I thought I'd better provide an authoritative cite but don't know if any of
this qualifies except for those who have fish ponds :-)) :
"Blanketweed after Rainstorms. Why should this happen?
We are certain it occurs, at least in part, because of something we have all
heard about. The key to this phenomenon is acid rain. I would suggest that
most of us have not fully appreciated the significance of acid rain in
keeping ponds. Acid rain arises from two types of acid-forming materials.
One is from sulphur dioxide that rises into the atmosphere primarily as a
byproduct of industrial processes and from the burning of fossil fuels. From
a pond keeping and algae growth perspective, these sulphur products are not
important.

The second acidforming group of gases that rise into the atmosphere are the
nitrogen oxides. These include nitric oxide (NO) and nitrogen dioxide (NO2).
When these oxides (NOx) are dissolved in rainwater high in the atmosphere,
mainly nitric acid (HNO3) is produced. This dilute acid falls to the ground
when it rains and produces nitrate in ponds.

The sudden rush into growth of blanketweed after a rainstorm is therefore
explained.

Another nitrogen compound that drops out of the sky when it rains is
ammonia. It falls to the ground and into ponds as dilute ammonium hydroxide
(NH4(OH)). It is an alkali, not an acid and the amounts are generally less
significant for pondkeepers than is the nitrate arising from nitric acid. It
is interesting to see that ammonia, one of the products pondkeepers are
removing from pondwater through their filters, can appear in the pond water
when it rains as well as from fish excrement.

The National Atmospheric Emissions Inventory
The website (www.naei.org.uk) of the National Atmospheric Emissions
Inventory (NAEI) gives a good deal of information about the amounts and
sources of various atmospheric pollutants by geographical region. Another
set of data that is available from the NAEI website is a table that shows
the annual tonnes of different pollutants emitted from various large point
sources situated within different distances from a particular postcode. Much
of the data has been produced from models used by the NAEI although some
have been provided by the owners of the plants in question.

Pondkeepers can access this tool by going to
www.naei.org.uk/mapping/mapping_2004.php and entering their postcode in the
appropriate box. We suggest that pondkeepers go into the NAEI website and
look further into the emissions that might be personally affecting them by
using their specific postcodes.

Going back to the original question of whether tapwater or rainwater should
be used for topping up ponds, the recommendation is the pondkeeper should
check particularly for nitrate (and other nasties) in both types of water
sources and, if possible, use the one with the lowest content. Pondkeepers
also have to bear in mind that levels may fluctuate so regular checking is
advisible. Better still, if pondkeepers practise water changes to simply
lower the nitrate level in the pondwater, then they need not change large
volumes of water because pond products, for example VirescoT, are available
that will take the nitrate level down to zero and hold it there. Once
nitrate is removed, blanketweed and other algae stop growing. However, there
is no substitute for keeping on top of regular pond husbandry."
http://www.practical-water-gardens.c...ateinwater.htm