| Year | Sufficient water quality | Good water quality |
|---|---|---|
| 2000 | 98.4615384615385 | 91.5384615384615 |
| 2001 | 97.7099236641221 | 87.7862595419847 |
| 2002 | 97.7099236641221 | 84.7328244274809 |
| 2003 | 96.9465648854962 | 84.7328244274809 |
| 2004 | 97.7099236641221 | 87.7862595419847 |
| 2005 | 96.1832061068702 | 90.8396946564885 |
| 2006 | 96.9465648854962 | 90.0763358778626 |
| 2007 | 96.9465648854962 | 80.1526717557252 |
| 2008 | 93.1297709923664 | 77.8625954198473 |
| 2009 | 93.1297709923664 | 82.4427480916031 |
| 2010 | 96.9 | 90.1 |
| 2011 | 98.5 | 83 |
| 2012 | 97 | 66.9 |
| 2013 | 96.8 | 84.4 |
| 2014 | 94.1 | 86.7 |
| 2015 | 93.4 | 83.2 |
| 2016 | 92.9 | 85.8 |
| 2017 | 93 | 84.5 |
| 2018 | 94.5 | 86.2 |
| 2019 | 95.2 | 89.1 |
During the 2000-2019 period more than 80% of bathing sites surveyed in Ireland had good water quality, except for 2008 and 2012. Over 90% of sites surveyed had sufficient water quality over this period.
In 2019, 89.1% of bathing water sites surveyed had good water quality and 95.2% had sufficient water quality.
| Year | Compliance of public water supplies with THM standard | Compliance of public group water supplies with THM standard | Compliance of private group water supplies with THM standard |
|---|---|---|---|
| 2009 | 87.4 | 70.4 | 89.4 |
| 2010 | 89.3 | 76.2 | 85.5 |
| 2011 | 91 | 87.1 | 93.6 |
| 2012 | 87 | 60.3 | 93.8 |
| 2013 | 92.1 | 79.8 | 94.4 |
| 2014 | 93 | 93.1 | 93.3 |
| 2095 | 91.5 | 87.2 | 95.7 |
| 2016 | 93.1 | 95.7 | 90.9 |
| 2017 | 94.3 | 96.6 | 96 |
| 2018 | 95.1 | 87.9 | 95.1 |
The quality of public water supplies as measured by compliance with E.coli standards has increased from an average annual 98.9% in 2004 to 99.9% in 2018. Compliance of public group water supplies has increased from 96.2% to 100.0%, while compliance of private group water supplies has increased from 78.1% to 98.5% over the same period.
The compliance rate of public water supplies for trihalomethanes (THM) has increased slightly from an average annual 87.4% in 2009 to 95.1% in 2018. The compliance rate of public group water supplies increased from 70.4% in 2009 to 87.9% in 2018, while the compliance of private group water supplies increased from 89.4% to 95.1% over the same period.
| Year | No treatment/preliminary treatment | Primary treatment | Secondary treatment | Secondary treatment with nutrient reduction |
|---|---|---|---|---|
| 1997-1999 | 41 | 33 | 21.5 | 4.5 |
| 2000-2004 | 30.5 | 21.5 | 39.5 | 8.5 |
| 2005-2009 | 10.3333333333333 | 1.33333333333333 | 74.3333333333333 | 14 |
| 2010-2014 | 5.08 | 1.52 | 70.44 | 23 |
| 0 | 0 | 0 | 0 | |
| 2015 | 4.2 | 1 | 68.3 | 26.5 |
| 2016 | 2.7 | 1.3 | 69.4 | 26.6 |
| 2017 | 2.2 | 1.2 | 66.6 | 30 |
| 2018 | 1.54 | 1.03 | 67.24 | 30.18 |
| 2019 | 1.44 | 1 | 67.17 | 30.39 |
There has been a significant improvement in the level of treatment of urban waste water in agglomerations of over 500 persons. In 2019, 30.4% of urban waste water received secondary treatment with nutrient reduction compared with only 4.0% in 1997. Only 1.4% of urban waste water received either no treatment or preliminary treatment in 2019, compared with 46.0% in 1997.
The percentage of unpolluted river water decreased from an average annual 77.3% in 1987-1990 to 66.2% in 2016-2018.
The percentage of slightly polluted river water has increased from an average annual 12.0% in 1987-1990 to 22.4% in 2016-2018. The proportion of moderately polluted river water increased from an average annual 9.7% in 1987-1990 to 11.2% in 2016-2018.
The level of seriously polluted river water has fallen from an average annual 0.9% in 1987-1990 to 0.2% in 2016-2018.
There was a mixed picture concerning groundwater quality standards in Ireland as measured by the quantity of nitrates detected by monitoring stations over the 1995-2019 period.
The proportion of samples with low volumes of nitrates (less than 5 mg/l NO3 milligrams per litre of nitrates) in groundwater increased from an average annual 16% in 1995-1997 to 29% in 2016, before falling to 20% in 2019.
However, the proportion of samples with higher nitrate levels (more than 25 mg/l) also increased from an average annual 20% in 1995-1997 to 23% in 2019.
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