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How Bore Depth Affects Water Quality: What You Need to Know Before Drilling

When drilling a water bore, many people assume that deeper is always better. After all, it seems logical—if you go deep enough, you’ll find a clean, abundant water supply, right? Not necessarily. The relationship between bore depth and water quality is far more complex and depends on local geology, aquifer conditions, and surrounding land use.

Understanding these factors before drilling can save you from costly mistakes and ensure you get the best possible water quality for your needs.

How Bore Depth Impacts Water Quality

1. Shallow Aquifers: Fresh but Vulnerable

Water found at shallower depths (less than 50m) often comes from recent rainfall and surface water infiltration. These shallow aquifers can be great sources of fresh, high-quality water, but they also come with risks:

✅ Lower salinity – Often fresher than deeper groundwater
✅ Easier and cheaper to access – Requires less drilling and lower energy costs for pumping
More susceptible to contamination – Can be affected by pesticides, fertilisers, animal waste, and industrial runoff
Seasonal variability – Water tables in shallow aquifers fluctuate, which means they can run dry during droughts

If you’re drilling in an area with agriculture, industry, or high population density, shallow bores may be at greater risk of contamination from nitrates, bacteria, and chemicals.

2. Deep Aquifers: Stable but Possibly Salty

Deeper groundwater sources (50m – 300m+) often contain water that has been underground for hundreds or even thousands of years. This water has percolated through layers of rock and sediment, undergoing natural filtration.

✅ More protected from contamination – Less affected by surface pollutants
✅ More consistent water supply – Less impacted by seasonal rainfall
Higher risk of salinity – Water may have picked up minerals, salts, and metals from surrounding rocks
Harder and more expensive to pump – Requires more energy and stronger pumps
Longer recharge times – Once depleted, deep aquifers take centuries to refill

In some regions, deeper water sources can contain high levels of iron, manganese, or arsenic, which require filtration and treatment before use. Bores drilled too deep may also tap into saline or brackish water, making them unsuitable for drinking or irrigation.

How to Determine the Best Depth for Your Bore

Since the ideal bore depth depends on local conditions, here are some steps to take before drilling:

1. Conduct a Hydrogeological Survey

A professional hydrogeologist can assess underground water sources, identifying the most reliable and high-qualityaquifer for your needs. This includes:
✔ Studying geological maps and water bore records
✔ Identifying the depth of fresh vs. saline water
✔ Analysing water recharge rates

2. Check Nearby Bore Data

In Australia, bore logs and water quality reports are often publicly available. Researching existing bores in your area can provide valuable insights into:

  • Typical water depth
  • Water quality reports (salinity, pH, hardness)
  • Seasonal fluctuations

3. Consider Water Use and Filtration Needs

  • If the bore is for household drinking water, prioritise low-salinity, low-contaminant aquifers
  • If it’s for irrigation, slightly higher salinity may be acceptable, but avoid high levels of iron or salt
  • For livestock, test for nitrates and heavy metals that could affect animal health

Striking the Right Balance

So, is a deeper bore always better? Not necessarily. The best bore depth is the one that provides reliable, clean waterwith minimal contamination and manageable pumping costs. Drilling too shallow can lead to contamination issues, while going too deep can introduce salinity and mineral concerns.

Before investing in a bore, do your research, test the water, and consult experts. A well-planned bore can provide decades of clean, sustainable water, while a poorly placed one can lead to costly filtration, pump maintenance, and even total failure.

Thinking about drilling a bore? Get the right depth for the right water—because what’s underground matters just as much as what comes out of the tap.