Wastewater vs Stormwater: What's the Difference?

Most New Zealand properties have two completely separate drainage systems: wastewater and stormwater. While both involve drains and pipes, they serve entirely different purposes, go to different places, and are subject to different regulations.

Understanding these systems helps you maintain them properly, avoid legal issues, and make informed decisions about drainage work on your property.

What is Wastewater?

Wastewater (also called sewage or sanitary waste) is water that has been used and contaminated by human activities. It contains waste products, chemicals, and potentially harmful bacteria.

Sources of Wastewater

Wastewater comes from:

Toilets: Human waste and toilet paper
Bathrooms: Water from showers, baths, and bathroom sinks
Kitchens: Water from kitchen sinks and dishwashers
Laundries: Water from washing machines and laundry tubs

Essentially, any water that goes down a drain inside your home is wastewater.

Where Wastewater Goes

Wastewater follows one of two paths:

1. Council Wastewater System: In urban areas like Kerikeri township or Paihia, wastewater flows through pipes to council wastewater treatment plants. The council treats this water before discharging it safely into the environment.

2. Private Septic Systems: In rural areas without council connections, wastewater goes to private septic tanks on your property. The septic tank separates solids and liquids, then disperses treated liquid into drain fields where soil bacteria complete the treatment process.

Why Wastewater Requires Treatment

Wastewater contains:

Human waste and associated pathogens
Harmful bacteria and viruses
Chemicals from cleaning products
Food waste and grease
Pharmaceuticals and personal care products

Without proper treatment, wastewater poses serious health and environmental risks. That's why it must be collected and treated before returning to the environment.

What is Stormwater?

Stormwater is rainfall runoff from roofs, driveways, paths, and other hard surfaces on your property. Unlike wastewater, stormwater starts relatively clean - it's just rainwater that hasn't soaked into the ground.

Sources of Stormwater

Stormwater comes from:

Roofs: Rain collected by gutters and downpipes
Driveways: Runoff from paved areas
Paths and patios: Water from hard landscaped surfaces
Yards: Surface water that doesn't soak into soil

Where Stormwater Goes

Stormwater disposal varies by location:

Council Stormwater System: In urban areas, stormwater drains to council stormwater pipes, which carry it to streams, rivers, harbors, or the ocean. Because this water goes directly to natural waterways with minimal or no treatment, it's crucial that only clean stormwater enters these systems.

Soakage on Property: In rural areas or where council systems aren't available, stormwater soaks into the ground on your property through:

Soakpits (gravel-filled holes that allow water absorption)
French drains (gravel-filled trenches)
Natural ground absorption
Discharge to waterways (with appropriate consent)

Why Keep Stormwater Clean

Although stormwater starts as clean rainwater, it can pick up pollutants:

Oil and chemicals from driveways
Fertilizers and pesticides from gardens
Sediment from construction sites
Litter and debris

Because stormwater often goes straight to natural waterways, preventing pollution of stormwater systems protects Northland's rivers, streams, and coastal waters.

Why These Systems Must Remain Separate

In New Zealand, it's illegal to mix wastewater and stormwater systems. Here's why:

Treatment Requirements

Wastewater needs extensive treatment before returning to the environment. Stormwater systems generally discharge directly to waterways without treatment. Mixing these systems would mean:

Untreated sewage entering rivers, harbors, and oceans
Contamination of beaches and swimming areas
Environmental damage to aquatic ecosystems
Public health hazards

System Capacity

Northland's high rainfall means stormwater systems handle large volumes during rain events. Wastewater systems are sized for the steady flow of household waste - not massive rainfall volumes. Mixing them would:

Overwhelm wastewater treatment plants during rain
Cause sewage overflows and backups
Flood homes with contaminated water

Economic Efficiency

Treating all stormwater to wastewater standards would be prohibitively expensive. Separate systems allow appropriate treatment for each water type, making infrastructure more cost-effective.

Legal Requirements in Northland

The Law is Clear

Under New Zealand's Building Act and council bylaws:

Wastewater and stormwater must be kept separate
Connecting wastewater to stormwater systems is illegal
Connecting stormwater to wastewater systems is illegal
All drainage connections require proper consents

Penalties for Non-Compliance

Illegally connecting these systems can result in:

Fines up to $200,000
Requirement to disconnect and rectify at your expense
Council prosecution
Liability for environmental damage
Property sale complications

Common Misconceptions

"It All Goes to the Same Place"

Myth: Some people believe wastewater and stormwater both end up at treatment plants.

Reality: Wastewater goes to treatment plants. Stormwater usually goes directly to natural waterways. They are completely separate systems with different destinations.

"A Little Cross-Connection Won't Matter"

Myth: Minor connections between systems are harmless.

Reality: Even small cross-connections cause problems. One house's wastewater entering stormwater systems can contaminate swimming beaches. Multiply that by many properties and environmental damage becomes severe.

"Older Properties Don't Need to Comply"

Myth: Older homes built before separation was required don't need separate systems.

Reality: While some older properties may have combined systems that were legal when installed, they must be separated when renovations occur or when council requires upgrades. The requirement for separation applies to all properties.

How to Tell Which System is Which

On your property:

Wastewater System Indicators

Connects to toilets, bathrooms, kitchens, laundries
Goes to gully traps (inspection chambers with water-filled traps)
May have a septic tank (if not connected to council sewer)
Pipes are typically darker colored (older properties may have clay pipes)

Stormwater System Indicators

Connects to roof gutters and downpipes
Drains hard surfaces like driveways
May discharge to visible soakpits or drains
Doesn't connect to any indoor fixtures

Proper Connections: What Goes Where

Wastewater System Should Receive:

Toilet waste
Shower and bath water
Bathroom and kitchen sink water
Washing machine discharge
Dishwasher discharge

Stormwater System Should Receive:

Roof water (from gutters/downpipes)
Driveway surface water
Path and patio drainage
Surface water from yards

Never Connect to Either System:

Swimming pool or spa discharge (requires special disposal methods)
Industrial effluent (requires trade waste approval)
Contaminated groundwater (requires environmental consent)

Special Considerations in Northland

High Rainfall

Northland's high rainfall puts extra stress on both systems:

Stormwater systems must handle high volumes
Infiltration into wastewater systems can cause overflows
Proper separation is even more critical during heavy rain

Coastal Areas

Properties near the coast face additional considerations:

Stormwater often discharges to harbors and ocean
High water tables affect wastewater disposal (especially septic systems)
Environmental protection requirements may be stricter

Rural Properties

Rural properties without council connections need:

Properly designed septic systems for wastewater
Adequate land area for stormwater soakage
Careful system design to account for local soil conditions

When You Need Professional Help

Call a licensed drainlayer when:

Installing new drainage systems
Modifying existing systems
Connecting to council infrastructure
You're unsure which system a drain connects to
Building or renovating
Experiencing drainage problems
Council has identified cross-connections requiring correction

Licensed drainlayers understand system requirements, can identify improper connections, and ensure all work meets legal and building code standards.

Protecting Northland's Environment

Proper separation of wastewater and stormwater systems protects:

Beaches: Keeping sewage out of swimming areas
Harbors: Protecting marine ecosystems and shellfish beds
Rivers and streams: Maintaining water quality for aquatic life
Groundwater: Preventing contamination of water supplies
Public health: Reducing disease transmission risks

Understanding and respecting the difference between these systems is part of responsible property ownership in Northland.

Summary: Key Takeaways

Wastewater = water from toilets, sinks, showers (contaminated, needs treatment)
Stormwater = rainwater from roofs and hard surfaces (relatively clean)
Must be separate by law - never mix these systems
Different destinations: Wastewater to treatment; stormwater to waterways or soakage
Professional installation: Licensed drainlayers ensure legal compliance
Environmental protection: Proper separation protects Northland's water quality

When in doubt about your drainage systems, contact Impact Drainage. We'll ensure your wastewater and stormwater systems are properly separated, legally compliant, and protecting both your property and Northland's environment.