Water Quality Fundamentals
Understanding groundwater chemistry and drinking water standards.
Why Water Quality Matters
Groundwater quality determines whether extracted water is safe for drinking, suitable for irrigation, or usable for industrial processes. Natural geological processes and human contamination can introduce substances that affect health, taste, appearance, and equipment longevity.
Key Parameters
| Parameter | WHO Limit | EPA MCL | Health Effect | Common Source |
|---|---|---|---|---|
| TDS | <600 mg/L | <500 mg/L | Taste, laxative effect | Mineral dissolution |
| Hardness | — | — | Scaling, soap waste | Ca²⁺, Mg²⁺ from limestone |
| pH | 6.5-8.5 | 6.5-8.5 | Corrosion, taste | CO₂, organic acids |
| Iron (Fe) | 0.3 mg/L | 0.3 mg/L | Taste, staining | Pyrite, iron-rich formations |
| Manganese (Mn) | 0.1 mg/L | 0.05 mg/L | Taste, staining, neuro | Manganese minerals |
| Nitrate (NO₃⁻) | 50 mg/L | 10 mg/L | Blue baby syndrome | Fertilizer, septic systems |
| Arsenic (As) | 0.01 mg/L | 0.01 mg/L | Cancer, skin lesions | Volcanic rock, mining |
| Fluoride (F⁻) | 1.5 mg/L | 4.0 mg/L | Dental/skeletal fluorosis | Volcanic rock, apatite |
| Total Coliform | 0 CFU/100mL | 0 CFU/100mL | Pathogen indicator | Surface contamination |
| Turbidity | <1 NTU | <1 NTU | Pathogen hiding | Sediment, drilling damage |
Watch: Water Quality Fundamentals
Key parameters for assessing drinking water quality: pH, hardness, dissolved solids, and contaminants.
Watch on YouTube ↗Testing & Analysis
Methods and protocols for evaluating groundwater quality.
When to Test
- New well (construction): Full analysis before first use — establishes baseline quality
- Annual monitoring: Bacteriological + select chemical parameters
- After flooding: Full bacteriological testing — contamination risk high
- Taste/odor changes: Investigate cause — may indicate new contamination or well deterioration
- Nearby land use changes: Agricultural, industrial, or construction activity nearby
Sampling Methods
- Purge and sample: Pump 3-5 well volumes before sampling to ensure representative water
- Low-flow sampling: Minimal disturbance — preferred for dissolved metals and volatile organics
- Grab sample: Simple but may not represent aquifer conditions
Laboratory Analysis
| Test Package | Parameters | Cost Range | Recommended For |
|---|---|---|---|
| Basic | pH, TDS, hardness, coliform, nitrates | $50-100 | All new wells, annual monitoring |
| Standard | Basic + iron, manganese, chloride, sulfate, fluoride | $100-200 | Domestic wells, agricultural |
| Comprehensive | Standard + metals, minerals, nutrients | $200-500 | Municipal supply, suspected contamination |
| Full panel | All EPA primary + secondary standards | $500-1000 | Regulatory compliance, industrial |
Contamination Sources
Identifying and preventing groundwater contamination.
Figure 18: Groundwater contamination pathways from six common sources. Contaminants travel downward through the unsaturated zone via gravity and percolation, then spread laterally through the saturated aquifer following groundwater flow direction. Plume shape depends on contaminant type, aquifer permeability, and groundwater velocity. Proper well construction (grout seal, sanitary cap) is the primary defense against surface contamination entering the well.
Natural Contamination
- Geological dissolution: Arsenic from volcanic rock, fluoride from apatite, radon from uranium-bearing granite
- Saline intrusion: Saltwater in coastal aquifers (Ghyben-Herzberg relationship)
- Iron and manganese: Common in reducing (low-oxygen) groundwater environments
Anthropogenic Contamination
| Source | Contaminants | Pathway | Prevention |
|---|---|---|---|
| Septic systems | Nitrate, bacteria, viruses | Subsurface leaching | Proper setback distances, maintenance |
| Agriculture | Nitrate, pesticides, herbicides | Irrigation return flow | Best management practices, buffer zones |
| Industrial | Heavy metals, solvents, petroleum | Spills, underground storage tanks | Secondary containment, monitoring wells |
| Landfill | Leachate, heavy metals, organics | Liner failure | Double liners, leachate collection |
| Mining | Acid mine drainage, metals | Surface and groundwater flow | Pretreatment, containment ponds |
| Well construction | Surface water, bacteria | Poor seals, damaged wellhead | Proper grouting, sanitary caps |
Wellhead Protection
Maintain minimum setback distances from contamination sources: 30 m from septic systems, 60 m from livestock operations, 150 m from fuel storage. These are minimums — check local regulations for specific requirements.
Figure 15: Typical multi-stage water treatment system for well water. Raw water passes through sediment filtration (1), iron/manganese removal (2), water softening (3), and UV disinfection (4). Optional stages include acid neutralizers for low pH and reverse osmosis for dissolved contaminants (nitrates, TDS, arsenic). Each stage removes specific contaminants, producing safe drinking water.
Treatment Systems
Methods for treating groundwater to meet drinking water standards.
Treatment Technologies
| Contaminant | Treatment Method | Mechanism | Cost Range |
|---|---|---|---|
| Hardness | Ion exchange (softener) | Ca²⁺/Mg²⁺ → Na⁺ exchange | $500-2000 |
| Iron/Manganese | Oxidation + filtration | Aeration, greensand, Birm | $800-3000 |
| Nitrate | Ion exchange, reverse osmosis | Selective removal | $1000-5000 |
| Arsenic | Adsorption (activated alumina, GFH) | Surface binding | $2000-5000 |
| Bacteria | UV disinfection, chlorination | DNA damage / oxidation | $500-2000 |
| Multiple contaminants | Reverse osmosis | Membrane filtration | $1500-5000 |
| TDS / Salinity | Reverse osmosis, distillation | Selective permeability | $2000-10000 |
| pH adjustment | Acid injection or alkaline media | Chemical neutralization | $500-2000 |
System Design Considerations
- Flow rate: System must handle peak demand (morning showers, irrigation startup)
- Waste stream: RO generates 20-50% reject water — requires drainage plan
- Maintenance: Filter media replacement, membrane cleaning, UV lamp replacement
- Monitoring: Regular testing to verify system performance
- Regulatory: Some treatment systems require permits or certifications
Water Softener Sizing:
Grain capacity = Daily hardness (gpg) × Daily usage (gallons)
Resin bed size = Grain capacity / Exchange capacity (30,000-45,000 grains/ft³)
Grain capacity = Daily hardness (gpg) × Daily usage (gallons)
Resin bed size = Grain capacity / Exchange capacity (30,000-45,000 grains/ft³)