Grey water, also known as sullage, is gently used water from household uses such as washing dishes, laundry, and bathing. Grey water differs from black water in the amount of contaminants present. Black water contains sewage and waste from toilets, while grey water generally does not contain major pathogens. Proper storage and usage of grey water reduces strain on water systems and facilitates water conservation.
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Why store grey water?
There are several benefits to storing and reusing grey water:
- Reduces strain on water systems – Capturing grey water onsite reduces the amount of fresh water needed from main water lines and septic tanks. This conserves water and reduces strain on infrastructure.
- Facilitates water conservation – Stored grey water can be reused for non-potable purposes like irrigation and toilet flushing. This reduces overall household water usage.
- Nutrient recycling – Grey water contains traces of phosphorus and nitrogen from soaps and detergents. When used for irrigation, these nutrients are fed back to soil and plants.
- Financial savings – Reducing household water usage through grey water systems can lead to lower utility bills and costs.
- Environmental sustainability – By reducing water withdrawals and recycling nutrients, grey water storage promotes environmental sustainability.
The benefits of grey water reuse make it an important tool for water conservation, especially in areas prone to droughts or water shortages.
Is it legal to reuse grey water?
The legality of grey water reuse varies by state and local regulations. Some key legal considerations include:
- Permits – Many states require permits for constructing and operating grey water systems, even in residential settings.
- System requirements – There are often specifications for system components, storage tanks, filtration, and how the grey water can be used.
- Backflow prevention – Regulations prohibit cross-connection between potable drinking water and grey water plumbing.
- Usage – Reusing grey water for purposes like irrigation, toilet flushing, and laundry is typically approved but regulations vary.
- Discharges – Illegal dumping of excess grey water could result in fines. Proper drainage requirements must be met.
Always check state and local laws when planning a grey water system. Permitting and inspections may be required to comply with regulations.
Evaluating how much grey water you generate
The amount of grey water produced in a household can vary based on several factors:
- Number of occupants – More residents means more water used for showers, laundry, dishes, etc.
- Water-using appliances – Homes with high-efficiency washers and dishwashers may produce less grey water.
- Water fixtures – Low-flow showerheads and faucets reduce water usage and grey water production.
- Household habits – Behavior and frequency of activities like laundry, bathing, and dishwashing impact grey water volumes.
Here are some estimates for typical grey water generation:
- Showers – 25-40 gallons per day per person
- Bathtubs – 20-30 gallons per bath
- Bathroom sinks – 5-10 gallons per day per person
- Laundry – 15-30 gallons per load
- Dishwasher – 4-6 gallons per cycle
- Kitchen sinks – 5-15 gallons per day
Tracking your water usage or meter readings can provide real data on your household’s grey water production.
Choosing the right grey water system
Several types of grey water systems are available:
| System Type | Description | Cost |
|---|---|---|
| Laundry-to-landscape | Grey water from washing machine only; distributed via gravity or pump to landscape | $$ |
| Branched drain | Grey water from most sources; distributed by gravity via dedicated plumbing to reuse points | $$$ |
| Tank-based | Grey water collected in storage tank for pumping and pressurized reuse | $$$$ |
Key factors in choosing a system:
- Uses – The intended grey water uses (irrigation, toilet flushing, etc) impact the optimal system.
- Topography – Gravity-based distribution works best on sites with downhill slope. Tank systems are needed for flat terrain.
- Soil type – Fast-draining soil is required for subsurface irrigation from grey water.
- Climate – Freezing climates may require buried tanks and pipes.
- Budget – Simple laundry systems cost less than complex branched drain or tank configurations.
Consulting with experts is recommended to design the ideal system for your site conditions and needs.
Storing grey water
Properly storing grey water is crucial for sanitary and safe reuse. Here are key storage principles:
- Use enclosed tanks or reservoirs specifically designed for non-potable water. Old food containers or open ponds create hazards.
- Prevent light exposure and algae growth by using opaque, UV-resistant plastic tanks or wrapping transparent tanks.
- Equip tanks with secure lids and screens to keep out debris and mosquitoes.
- Include valves and drains to facilitate maintenance and cleaning.
- Use durable materials like concrete, wood, or polyethylene that won’t corrode or leach chemicals.
- Locate tanks according to local codes, avoiding areas prone to flooding or freezing.
Tanks should be sized appropriately for the intended uses and projected grey water volumes. Most residential systems require 500-3000 gallon storage capacity.
Grey water filtration and disinfection
Additional filtration and disinfection of stored grey water helps reduce risks:
- Pre-filter screens – Coarse screens on tank inlet pipes exclude hair, lint, and debris that can clog systems.
- Sedimentation – Letting grey water sit allows suspended particles to settle on the bottom.
- Sand and mesh filters – Passed through layers of sand, fabric, or mesh to filter out particles.
- Activated charcoal – Charcoal media removes some organic contaminants and odors.
- UV disinfection – Ultrasound units kill bacteria and microorganisms without chemicals.
- Chlorine or hydrogen peroxide – Disinfecting chemicals can be carefully dosed to treat grey water.
Simple systems may utilize only coarse screening, while more complex installations incorporate progressive filtration and UV treatment. Proper tank cleaning is also vital.
Using grey water
Typical approved uses of treated grey water include:
- Subsurface irrigation – Grey water is distributed through drip irrigation lines or released into mulch basins to irrigate trees, shrubs, and ornamental plants.
- Surface irrigation – Spray or flood irrigation can utilize grey water for lawns, pastures, and other tolerant vegetation.
- Toilet flushing – Disinfected grey water can be plumbed into toilets for flushing use, greatly reducing potable water demand.
- Washing machines – Reusing grey water for the washing cycle further extends the supply.
Improper usages like spraying edible plants, surface ponding, and exposure to humans must be avoided. Follow all local regulations for approved applications.
Maintenance for grey water systems
Routine maintenance ensures proper functioning:
- Inspect and clean tanks at least annually, pumping out sludge and debris.
- Check and clean filters based on manufacturer recommendations.
- Inspect and flush pipes/emitters to prevent clogging.
- Monitor storage levels and pump operation.
- Watch soil moisture and drainage for irrigation areas.
- Test grey water quality for pH, sodium content, and pathogens if needed.
- Service mechanical components like pumps and disinfection systems per manufacturer instructions.
Keep detailed records of all maintenance activities. Upgrade or expand the system as needed based on usage and inspection results.
Troubleshooting common grey water system problems
| Issue | Potential Causes | Solutions |
|---|---|---|
| Blocked pipes or emitters | Debris buildup, algae growth | Flush lines, clean tanks and filters |
| Pungent odors | Excess organics, anaerobic conditions | Treat with enzymes, oxygenate tanks |
| Leaking tanks/pipes | Cracks, disconnected joints | Repair leaks, test for watertightness |
| Insufficient irrigation | Low storage volume, pump failure | Enlarge storage, repair/replace pump |
| Poor drainage | Soil compaction, small emitters | Aerate soil, use larger emitters |
| Excess salt accumulation | High sodium grey water, poor flushing | Source softening, leaching irrigation |
Conclusion
Grey water reuse provides major water savings for households when systems are properly designed, installed, and maintained. Choose an appropriate system for your site conditions, intended uses, and budget. Follow regulations for permitting, storage, treatment, and application to safely realize the benefits of grey water recycling.