Periodically we have to flush through our watering system to prevent the bacteria causing Legionnaires disease.  Legionnaires disease is waterborne and harmful to humans. It causes a pneumonia like lung infection.  It is caused by inhaling bacteria infected water droplets.  I thought it was a good time to flush the system today as it is the last day of my school holiday.

Below is a photo of our 16,000 litre rainwater tank which holds rainwater collected from the greenhouse roof.

The rain water is pumped into a holding tank within the greenhouse, where it is let to warm up to greenhouse temperature. This is because we do not want to shock the orchids, with cold water, when watering. Unfortunately this water is an ideal breeding ground for the Legionnaire bacteria. We cannot add chemicals to kill the bacteria as it would be injurious to the orchids.  Luckily our dark tank is inhospitable to algae growth on the inside.

I have not been refilling the holding tank with fresh rainwater, for the last few days after watering.  I left a little water in the tank so that the pump did not run dry. This residual water can now be removed by turning the tap at the bottom of the left hand side of the holding tank.

The water can now run freely away and not damage the pump.

Next it is time to turn off the tap which allows the water to come from the outside rainwater tank, into the holding tank.  This is the larger of the two taps.  The vertical position shows it is off.  The smaller tap, when vertical, allows mains water to flow into the system.

The empty holding tank is now being flushed through with chlorinated mains water.  It should do this for at least half an hour.

After half an hour has gone by the mains water can be turned off. Do this by turning the smaller tap to the horizontal position.  Turning the larger tap to the horizontal position allows the rainwater to flow into the  holding tank, when the irrigation pump is turned on.

It is now time to turn off the tap at the bottom left of the holding tank.  This stops it emptying when fresh rainwater is pumped in.

Turning on the irrigation pump allows the rain water, held in the outside tank, to be pumped inside to the holding tank.  This will take at least an hour.

When the holding tank is full turn off the irrigation pump.