is usually very clean - drinkable, in fact. Unfortunately,
we live in a very dirty world so when rain falls on something,
it picks up dirt. I'm not goin gto use my rain barrels as a
source of drinking water but I do want the water to be clean.
So, to help clean the water headed to the barrels I put a first
flush device just upstream from the barrels.
In between rains dirt accumulates on surfaces.
This dirt is washed away when it rains but it is not washed
away evenly; early runoff is much dirtier than later runoff.
Knowing that the beginning of a rainfall is where most of the
dirt is, I built a first flush device (FFD) to divert the
first ~5 gallons of rainwater from the barrels. This diversion
prevents a large amount of dirt from getting into the barrels.
There are many different ways of building
FFDs and you can buy them too but buying one would be no fun.
In designing/building my FFD I wanted low to no maintenance,
few to no moving parts and an elegant design. We're always
looking for the elegant solution...
Most FFDs I saw are very simple devices
but many seem overly complex, require a lot of attention and/or
have too many moving parts. The design I settled on is essentially
a long tube with a small ball in it (I'll add a detailed diagram
in the future). The tube is about 5 gallons in volume and placed
between the collection surface (my roof) and the barrels. At the bottom of the tube I have a spigot
which I keep cracked open slightly so it takes 5-10 hours for
the tube to fully drain.
When it begins raining the first five
gallons of water does not get to the barrels, it fills the
tube. Once the tube is full the ball floating in it blocks
off the top (think of a ping pong ball in a 2 liter bottle
- when the bottle is almost full, the ball will block more
liquid from entering the bottle). With the tube full and the
top blocked, the rainwater then is free to fill the barrels
with cleaner water. The spigot at the bottom slowly drains
the tube but it doesn't take much rain to continually top off
the tube. When the rain stops the tube slowly drains
until empty and is ready for the next rainfall.
Coming in the future: diagrams, materials,
building instructions and more photos.