Grey water — the wastewater from showers, sinks, baths, and washing machines — makes up around 50–80% of household wastewater. With proper treatment, it can be recycled back into the home for flushing toilets, watering gardens, and other non-potable uses. Herr Ltd designs natural, low-energy grey water recycling systems for Irish homes, helping reduce mains water use, lower water bills, and build resilience against the longer summer droughts now expected in Ireland.

Our systems are ideal for new builds, deep retrofits, and rural one-off homes — particularly where water conservation, planning sensitivity, or off-grid living are priorities.

Why Recycle Grey Water in Ireland?

Cuts mains water use by up to 40% — Grey water can flush toilets and supply garden taps without ever using treated drinking water.
Drought resilience — Irish summers are becoming hotter and drier. Recycled grey water keeps gardens alive and toilets flushing during hosepipe bans.
Lowers water charges — For non-domestic users and any future household charges, less mains water in means less wastewater out.
Reduces pressure on septic tanks — Diverting grey water from the septic system extends its life and reduces overflow risk.
Supports planning applications — Particularly in pollution-sensitive areas or sites with poor percolation.
Pairs perfectly with rainwater harvesting — Together, they can supply most or all non-potable household water.

What is Grey Water?

Grey water is all household wastewater except that from toilets and (in some definitions) kitchen sinks:

Included — Showers, baths, hand basins, washing machines.
Sometimes included — Kitchen sinks and dishwashers (these contain more food solids and grease, so usually need additional pre-treatment).
Excluded — Toilet wastewater (this is “black water” and requires full treatment — see our reed bed and composting toilet systems).

How Grey Water Recycling Works

Herr Ltd grey water systems use natural processes — gravity, plants, soil, and microbes — wherever possible:

Step 1 — Collection — Grey water is collected from showers, baths, and basins via a separate plumbing line.
Step 2 — Pre-treatment — A settling tank removes hair, lint, and fine solids.
Step 3 — Biological treatment — Treatment in a small reed bed, sand filter, or planted gravel filter removes organic matter and pathogens.
Step 4 — Storage — Treated water is stored in a buffer tank for reuse.
Step 5 — Reuse — Pumped (or gravity-fed where possible) to toilets, washing machines, and outdoor taps.

Most of our designs avoid pumps and electrical components wherever the site gradient allows.

Typical Uses for Recycled Grey Water

Toilet flushing — The single biggest non-potable demand in most homes.
Washing machines — With suitable filtration.
Garden irrigation — Lawn, beds, and (with care) vegetable plots.
Outdoor cleaning — Driveways, patios, paths, and cars.

Benefits for Irish Homes and Sites

Ideal for terraced houses, urban infill, and new builds — Where garden space is limited and rainwater alone may not be enough.
Excellent fit for off-grid and rural sites — Combined with rainwater harvesting and composting toilets, near-total water independence is achievable.
Low operating cost — Gravity-fed systems use little or no electricity.
Long system life — Few moving parts means decades of reliable service.

Designing Your Grey Water System

The right system depends on:

Household size — Number of occupants drives flow volumes.
Site gradient — Sloping sites suit gravity-fed designs; flat sites may need a small pump.
Available outdoor space — Reed beds and planted filters need a small footprint of garden.
Intended reuse — Garden-only systems are simpler than those plumbed back to toilets.
Other systems — Whether grey water will pair with rainwater harvesting, a reed bed, or a composting toilet.

We design each system from the ground up for the specific site.

Regulations in Ireland

Grey water recycling is permitted across Ireland under existing wastewater and building frameworks:

EPA Code of Practice for Domestic Waste Water Treatment Systems (2021) — Recognises grey water separation and reuse as supporting reduced discharge volumes. View the 2021 Code of Practice
Building Regulations – Technical Guidance Document H — Covers drainage and wastewater. Recycled grey water for toilet flushing is permitted where dual plumbing and clear labelling are in place. View Technical Guidance Document H

In Northern Ireland, the Building Regulations (NI) 2012 (as amended) and DAERA pollution-prevention guidance permit grey water recycling under similar performance-based standards.

For new builds, include grey water plumbing in your planning application — it is far cheaper to install during construction than to retrofit.

Why Choose Herr Ltd?

Over 30 years’ experience in ecological water and wastewater design across Ireland.
Low-energy, plant-based systems — Designed to last decades with minimal maintenance.
Whole-home design — Grey water works best as part of a complete system. We can integrate it with reed beds, rainwater harvesting, and composting toilets.
Architect collaboration — We work with architects from the early design stages to build water efficiency into the project.
Compliance documentation — Full design and specification support for planning and Building Control.

Thinking about grey water recycling for a new build or retrofit? Get in touch for a site-specific consultation.

Grey Water Recycling