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Disinfection of Domestic Wells and Boreholes

on Tuesday, 04 July 2017. Posted in Blog, Property, Tillage, Sheep, Dairy, Beef

Reference:  This test method is based on the Geological Survey of Ireland Guidelines for disinfecting wells.  GSI Newsletter No.38, Dec2000.

N.B. This method is only suitable as a once off shock disinfecting procedure and cannot replace a proper treatment system if your water supply needs continuous disinfection.


Disinfection is an important means of protecting human health, but it should not be considered as a solution to groundwater contamination.  The Geological Survey of Ireland recommend that all new wells should be disinfected after drilling and that existing wells should be disinfected on a regular basis (each Autumn is suggested). 

There are two method recommended for the disinfection of boreholes; method 1 involves the use of bleach and method 2 involves using chloros.  Both methods are outlined below.


    • Method 1               Bleach (sodium hypochloride, 3-5% available chlorine) or Milton
    • Method 2               Chloros (12% available chlorine)
    • Mixing container.
    • Water.


Method 1               Using Bleach (sodium hypochloride, 3-5% available chlorine)

1             Obtain 2 gallons (9 litres) of 3% strength or 1 gallon (4.5 litres) of 5% strength e.g.Parazone or Milton.

2              Make up to 5 gallons (22.5 litres) by adding water and mix thoroughly.

3             If sampling during a pumping test, on the day before the test starts pour half of the solution into the borehole/well, start the pump and let it run briefly until water with a distinct smell of chlorine pours from the outlet pipe.  Turn off the pump immediately.  Add the remainder of the solution and leave overnight (12 – 24 hours).  Then pump to waste until the smell of chlorine disappears before taking a sample for analysis.

4             If sampling from a well that is connected to a house, pour half of the solution into the well, start the pump and open all taps until water from each tap has a distinct small of chlorine.  Stop the pump and add the rest of the solution.  Allow to stand for 12-24 hours, then pump to waste until the smell of chlorine disappears. The length of time it takes to pump a well completely depends on the volume of the well, the volume of bleach added and the size of the pump installed.

Method 2               Using Chloros (12% available chlorine)

1              Obtain 0.5 gallons (2-3 litres) chloros.

2, 3 and 4 as above.

Water usage

Water is the forgotten nutrient on farms and can be a massive expensive but a necessary one, to have thriving productive animals. The following is the necessary water per day

    • Dairy cow               90 litres
    • Dry/suckler cow  45 litres
    • Pigs                          20 litres
    • Ewe                           5 litres

If the animals are not getting access to this level of water per day then they will not be as productive as they are capable of. For example a dairy cow will drop in milk yield 10% without adequate water which in the average herd will be 500 litres of milk per year per cow. This is €132.50 per cow at current prices or over €6500 for the average herd size in the country. 

Water loss is even more expensive on farms and tends to be something that is forgotten about. A dripping tap can cost  between €2 and €40 per day depending on how bad the drip is. The usual cause of this is a worn washer which is a 70c fix and a 5 minute job.

A leaking ball valve in a drinker can lose up to 150000 litres of water a year believe it or not and will save you €170 per year if fixed.  An underground leak with a constant stream can be a lot worse costing anywhere up to €1500 per year. One example recently where a farmer replaced a length of piping where there was a leak at a cost of €450 for the materials and work. His saving in the first year was €1840

When installing new water system on your farm it is a good idea to future proof the system. Install valves at the start of each pipe leaving the meter on the central water pipe so if there is a leak then it can be isolated and dealt with. Always monitor water pressure on the farm and check your meter regularly. Turn off all water and check the meter has stopped moving. If there is no water being used and the meter is still moving then there is a problem some where

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