GREY WATER RECYCLING
Grey water recycling is a process whereby you re-use your bath/shower and basin water for another purpose.
With the water shortage in South Africa getting worse from year to year, it leaves one wondering how long fresh potable water will be freely available. If you have not begun re-using your grey water as of yet, just try imagine 1 week without water freely running out your taps.
Gravity Graywater Filter (No pump)
Features of Aqua2use Graywater System ONLY FOR GRAVITY OPERATION The Aqua2use Graywater System uses the Matala 3D progressive filtration technology:
- Progressive 4 Stage Filtration.
- Cross-Flow depth filtration: each filter web has a 3-dimensional structure, able to trap a high volume of impurities without plugging.
- Multichamber plug flow concept: If the first filter web gets clogged the filtration is done by the 2nd and 3rd filter web. If the second web gets clogged, the filtration is done by the 3rd filter web.
- Easy to install: Connect your graywater pipe to the unit and attach your irrigation line to the drain.
- Sufficient height installation required (minimum of 4 feet high).
- Low maintenance – Easy cleaning every 4 to 6 months.
- Can also be used as a rainwater filter to remove debris before entering a rainwater collection tank, or direct supply to the IrriGRAY graywater/rainwater dripper line system.
- Dimensions: 24″ L x 15″ W x 20″ H
DIY Grey Water Kit (Pumped)
This unit works with a built-in pump, to pump the water into the garden. The pumped unit is ideal for the homeowner with bathrooms that are lower than some parts of the garden.
Key Features:
- Durable housing with UV protection.
- All fitting supplied for installation.
- Built in easy 3way diverting system, totalling 8 mats.
- Built in overflow safety device.
- Built in submersible pump with EPC.
- Pump has built in run dry and clogging detection.
- Easy to clean weir.
- Easy to assemble and installation instructions.
QUESTIONS ABOUT GREY WATER
Any used wash water in the home, except water from toilets, is called grey water. Shower, laundry, and sink water comprise 50-80% of residential “waste” water. This may be reused for other purposes, especially landscape irrigation.
NB: Kitchen sink water is classified as “dark grey water” and is only suitable for harvesting if the correct system is set in place. We caution against harvesting kitchen sink water due to blood and meaty fats present.
The benefits of using grey water
It’s a waste to irrigate with great quantities of perfectly good drinking water when plants thrive on used water containing small bits of compost and organic waste. Unlike a lot of ecological stopgap measures, grey water reuse is a part of the fundamental solution to many ecological problems and will probably remain essentially unchanged in the distant future. The benefits of grey water recycling include:
- Lower fresh water and/or drinking water usage.
- Less strain and costs on failing septic tank or treatment plant’s
- Better treatment (topsoil is many times more effective than subsoil or treatment plant)
- Less energy and Less chemical’s to treat sewage
- Groundwater recharge
- Massive improvement on Plant growth
- Reclamation of what would have been wasted nutrients
- Increased awareness of and sensitivity to natural cycles
- With the correct system installed grey water can be used for washing machine and toilet cistern water
The importance of grey water
In a nutshell, grey water systems don’t look that important. A new low flow shower head can save you water with less effort. A septic tank system can treat grey water almost as well. But when you look at the bigger picture and how everything connects to one another, the keystone importance of grey water is revealed.
Ecological systems design is about context, and integration between systems. The entirety of integrated, ecological design can be reduced to one sentence: do what’s appropriate for the context.
Ecological systems such as : rainwater harvesting, runoff management, passive solar, composting toilets and edible landscaping, all of these are more context sensitive than their counterparts in conventional practice; that’s most of what makes them more ecological.
Grey water systems are more context sensitive than any other man-made ecological system, and more connected to more other systems.
Get the grey water just right, and you’ve got the whole package right, and that is what matters.
Many people and organizations instinctively recognize that grey water is the ideal test case for the transition to a new way of regulating and building that is appropriate to a post-peak resource, mature civilisation.
The US Green Building Council, the City of Santa Barbara, CA, Oregon ReCode, and SLO Green Build are among those organizations which independently chose grey water standards as the technology with which to launch their programs of regulatory reform.
Is it safe to reuse everyday grey water?
Yes. There are eight million grey water systems in the US alone with 22 million users. In 60 years, there have been 1 billion system user-years of exposure, yet there has not been one recorded case of grey water transmitted illness.
Is grey water legal?
In practice, grey water legality is hardly ever an issue for residential retrofit systems, everybody just bootlegs them. However, grey water legality is almost always an issue for permitted new construction sites and/or remodelling purposes. For any further information on a Grey Water Harvesting unit suited to your home’s needs, please feel free to contact us.
HOW TO USE HARVESTED GREY WATER
The reuse of greywater on gardens can be a valuable resource in times of drought but can also be unsafe for plants and soils. Other properties come from the quality of the drinking water into the home before it is contaminated as greywater. Not all town water supplies are the same. There is no standard for drinking water. This difference will be discussed when we talk about salinity. If on the other hand you are using rainwater, there is only minor salinity in the water and nearly all the contamination will come from the chemicals used in the home.
The most important considerations for reuse are: the quality of the greywater; the plants you will irrigate with the greywater; the soil in your garden; how much greywater you spread over a given area (measured in litres per square metre); how often you water the same area; and when it rains on the garden; and (I’ll explain how the most damaging effect of greywater reuse can be from rain, but more of that later.) enrichment of the irrigation area.
Let’s look at the reuse of water in the garden in some logical manner and follow the points outlined above. Of course, you will need to consider your individual aim of reusing greywater, whether it is just to keep plants alive until the drought breaks, or as a permanent means of reducing your dependence on drinking water (town water or tank water).
Remember – there is a difference between SALINITY (all salts) and SODICITY (sodium specifically). Many salts are good for the garden, and we will discuss the use of some of these in ameliorating the soil. Sodium usually leads to loss of soil structure and plant strength (even death).
Quality of Grey Water
The drinking water that comes into your home may be from town water supplies (treated, reticulated water that may be from rivers, bores or a mixture then treated with chemicals to remove suspended material, change the pH, amend the alkalinity and reduce the hardness as well as adding chlorine and fluorine); rainwater collected on roof tops and stored in plastic, galvanized or concrete tanks; or borehole water from basalt, sedimentary or basalt aquifers (various proportions of sodium, calcium and magnesium). Depending upon the source of water, you may already have an abundance of minerals to consider on top of the chemicals you will add in the home.
Town water supplies (reticulated water from water treatment plant)
The quality of water supplied by local authorities through the reticulated networks varies from locality to locality and much is dependent upon the landscape from which the water is collected. Some catchments have very hard water (difficult to lather) that must be softened before reticulation (water high in calcium and magnesium has those elements precipitated out), while other catchments may have high sodium that cannot be removed by precipitation and filtration.
Other chemicals are added to the water during treatment to assist in flocculating clays (aluminum salts) so that they can be removed by filtration, while other chemicals are added to adjust pH, to add fluoride and chlorine. All these salts affect the final product that you receive as reticulated water and have been developed with consideration of health and aesthetics and nothing at all to do with any potential future use of the water. In the same way that most household chemical manufacturers don’t consider how the water contaminated with their products may be used to irrigate soils.
From the figure above it is clear that the coastal town water supplies mostly have low levels of total dissolved solids (TDS), which can also be referred to as salinity (not sodicity) and the inland towns, mostly have higher TDS. So all water cannot be treated the same when it comes to judging what happens to the water when you turn it into greywater in the home. The harder the water, the more detergent you have to use to overcome the effects of the salts causing hardness before you even start to wash the clothes.
Rainwater generally has TDS less than 20 mg/L and to use the same quantities of laundry detergent as reticulated supplies is simply a huge waste of detergent. Unfortunately, I think the laundry product manufacturers base the quantity of detergents recommended for the urban areas and are not dealing with rainwater quality.
Borehole water or well water will be strongly influenced by the geology of the aquifer (water bearing stratum) from which it was sourced. Borehole waters are generally higher in TDS than town water supplies (except for some very special aquifers). Some borehole water would be better not used in the laundry because of the increased use of detergents that have to be used, and the potential that greywater will have for future plant and soil problems.
Plants in your garden
It is not our intention to give suggestions of plants that are suitable for greywater irrigation because climate, soil types, and garden care will play more substantial roles, and these vary widely across South Africa. What you need to consider is whether your garden has (a) been developed using low salinity town water and you only want to use greywater as an interim resource until water restrictions are lifted, or whether (b) you want your garden to be sustainable on greywater even when water restrictions are lifted. There is an economic incentive to reuse greywater, but it must be used wisely, or it will be a hazard to your garden.
Many plants are intolerant of high salinity, and even more plants are sensitive to sodium and that is because sodium affects the osmotic pressure in the plant cells (the ability to move water and minerals from the soil into the plants cells and hold the cells rigid, rather than move nutrients from the plant cells into the soil solution). Plants that are irrigated with water high in sodium will look like they need a drink, and in severe cases the leaf margins (around the edges of the leaf) will start to look scorched or burnt. When that happens, you have serious problems and using rainwater may not be the option as rainwater can make the problem of sodicity much worse.
The amount of phosphorus in the greywater may not be a problem as only a few plants are sensitive to high phosphorus levels. In many soils there is a natural system to halt the phosphorus and minimise the phosphorus available to plants from the soil solution. There is very little evidence that native plants are intolerant to phosphorus, except for perhaps the Proteaceae family, but that is a debatable issue for some gardeners. It is true though, that many Australian species have developed mechanisms to absorb phosphorus from soils that have exceedingly low natural levels of phosphorus, but when phosphorus is available, the plants thrive. If phosphorus kills native plants, then why is phosphorus as important to native plants as it is to all living things – including us?
When you discuss your plant selection with your local nursery, be specific when discussing sodium issues as this element will dominate in greywater. And don’t let your plant specialist convince you that sodium is the same thing as salinity – that is simply not true.
Soil in the garden
It would be unreasonable to think that only the quality of the greywater and the plants were important when considering reuse of greywater. More important is the soil type, soil horizons (the different layers of soil as you dig deeper), soil chemistry and soil microbiology. This is by no means a soil science lecture, but there are some topics you need to grasp so that you can make informed choices as to whether you reuse your greywater or not.
Soil is graded in a couple of ways. First, by the proportions of sand, silt and clay that are the mineral components based upon grain size and that classification is called “Soil Texture” and secondly by the “Structure” – the way the soil particles are grouped together.
SOIL TEXTURE – Simply we can refer to soils as sands, loams and clays and then give them descriptions like loamy sand, sandy loam, clay loam or light clay. So how do you tell what it is – that’s simple. Take some soil in your hand, as much as you can hold, add water slowly while manipulating the soil in your hand until you can work the soil into a ball, about the size of a golf ball.
SANDS – difficult to form into a ball, with visible sand grains.
LOAMS – easy to form into a ball, and the ball is quite smooth and spongy, not very sticky.
CLAYS – form into a ball that behaves like plasticine, sticky and you can roll some out into very fine ribbons
Soil classification is not as simple as that – there’s another couple of steps to determine the SOIL TEXTURE, but essentially, we are after the texture (feel) and behaviour of the moist soil.
The second classification we need is the SOIL STRUCTURE, that is, how are the particles in the soil glued together to form larger lumps, blocks, clods into what we call aggregates (or peds).
Dig a hole about spade width and spade depth, put all the soil to one side. Then down one side of the hole, take a spade full of soil about 75 mm thick, lift out that wedge of soil, and from about waist high, drop the soil onto a hard surface. Sort the soil into several grades – Move all the larger lumps towards one end, and all the mid-size lumps into the middle and all the smaller lumps to the other end. The figure opposite, from NZ field manual is an excellent illustration of how the soil can be classified.
Left hand photo: Wedge of soil dropped on ground (Photo: R.Patterson). Right-hand set: Reference: Soil Management Guidelines for Sustainable Cropping. TG Sheppard, CW Ross, LR Basher and S Saggar. Landcare Crown Research Institute, NZ. 2000
SANDY soils will not behave in the same way as the photos above because they are not strongly aggregated as in soils that have a moderate to high clay content.
The difficulty with SANDY soils is not a chemical problem but one of water moving through the soil too rapidly with insufficient time for the nutrients to be absorbed by the plants or adsorbed onto the soil minerals. On sandy soils the area must be increased to account for the poor soil nutrient status – you need to spread the greywater further so the plants can access the nutrients before they leach deeper into the soil profile.
Spreading water over the garden
The area over which you spread the greywater depends upon the salinity, sodicity and phosphorus levels in the greywater. Don’t worry about nitrogen because these levels are very low and significantly less than the plants require, even if spread by bucket over a small area. Plants require about 25 g N/m2 (read that as 25 grams of Nitrogen per square metre), 3 g P/m2, and about 40 g Na/m2. These levels are guides only and fluctuate from soil to soil, although the levels are very similar for most plants, except for sodium (Na) for sensitive plants.
How do you calculate the area over which you should spread the greywater? As these calculations can be difficult without having a lab analysis of both the greywater and the soil, in the table below are some examples of what area you may need to irrigate if you choose various detergents with low, medium or high phosphorus. The same has been done for sodium levels. This is a guide only and is based upon the laundry water contributing the major portion of these two elements. It is assumed that the family will do seven washes per week.
Suggestions for application areas for various levels of phosphorus or sodium based upon a clay soil.
As you can see from the table, you will always need much more land to spread the greywater because of the sodium compared with the phosphorus.
The above is a “best guess” for porousness in soils that have a loam surface soil over a clay subsurface. The porousness of the loam is expected to be reasonable while the porousness of the clay would be very slow. Therefore, the loading rate has to be less than the ability of the topsoil to infiltrate water.
As you can see from the above table, attempting to bucket water over the garden so that the greywater is spread evenly over the required area will be a enormous task and one that will become very tiring. Even to spread the greywater using an irrigation system will require considerable irrigation pipe and an appropriate pump.
There is a difference between “infiltration” and “porousness” and they do not mean the same thing. Infiltration is just a measure of how quickly water moves from the surface into the soil. Throw a bucket of water over the soil and see how quickly it disappears. Of course, it will infiltrate quicker if the soil is moist than if it is already wet. Some soils will be difficult to wet when they are very dry, and mulch often becomes water repellent and can be more harm than benefit to the plants. Porousness on the other hand is the rate that water moves through the soil and is a quality that we cannot see. We need special devices to measure this property.
For SANDY soils, the application area must be larger than the areas given in the above table because of the rapid porousness and the potential for the salts to move rapidly downwards to groundwater. Now that seems strange because the water will infiltrate into sands at a faster rate, and you would think the area could be smaller. Well, that’s only part of the solution, because what you are looking at achieving is spreading the chemicals (nutrients) in the greywater, so they do not damage the groundwater or the plants.
Frequency of irrigation
How frequently you go back to the same area depends again on the strength of the greywater and the soil type. The above table infers that the water is spread evenly over the whole area in a year. When the greywater is very strong (high salinity, high sodium, or high phosphorus) the frequency must be sufficient to ensure that the salts are leached through the soil by using excess greywater or waiting for rain. The problem is that in a home garden you cannot know when the salts are leaching out of the root zone. Therefore, more water is better. Except, the problem then arises when rainwater falls on the soil and is likely to mobilise the sodium and lead to soil structural problems. Now we are caught in a situation where we may be causing problems by irrigating too much, or problems from not irrigating enough. Where do we go?
Simple. If you are using a high sodium detergent, spread the greywater as far as you can – perhaps even further than indicated in the above table. You may need to enrich the soil with gypsum, lime or organic matter (composted materials) to reduce the loss of soil structure, as discussed below.
Rain of the garden
The real issue with using greywater that is high in sodium is that soil structural problems that arise are difficult to fix. The first sign of structural problems is that the surface of the soil sets a hard crust – harder than areas not irrigated with greywater. Another sign is that the greywater takes longer and longer to soak into the soil or that rainwater is now ponding in areas it has not ponded before. When digging in gardens that have been poorly treated with greywater, the soil will be very cloddy (that is, more cloddy than soil that has not received greywater). You should always be seeking simple answers – how has the soil changed after using greywater?
Soils high in sodium are likely to disperse in rainwater (middle photo below). The reason is complex and beyond the scope of this page to explain in scientific terms. What happens is that the individual clay particles separate and move into the soil solution and stay in suspension in the same way that smoke stays in the atmosphere for a long time. The individual clay particles can then move with moving soil water and these particles can block soil pores in the same way that a filter is blocked with solids. Finally, the soil will become so blocked with clay particles from above that the soil as a filter is blocked and water can only pass through very slowly, sometimes not at all and the soil becomes impervious. Dispersible soils have very hard-setting surfaces and this may be more pronounced when drying after rain rather than after greywater application.
You can test whether your soil is likely to disperse when rain wets the soil. Take some small soil aggregates, about 3-5 mm in diameter and dry them on some paper towel on the kitchen windowsill. When they are dry, place them in a tumbler of clean water.
Aggregates (left hand photo) usually slake (simply fall apart) because they have insufficient organic glues to aggregate the soil particles and slaking is typical of subsurface soils that are low in organic matter. This is not a serious problem provided there is sufficient organic matter for the particles to re-aggregate on drying. Soils that disperse (middle photo) are real problem soils and most of these soils have problems because of high sodium. The water stable aggregates (right hand photo) either do not change their size or shape or may swell but maintain their shape. Both these soils (class 7 and 8) are the types of performance we desire in good garden soils and require good management and plenty of organic material to encourage earthworms and the numerous species of bacteria and fungi that live in a favourable environment. Adding greywater may cause Class 7 or 8 soils to become class 1 or 2 soils, a most undesirable outcome.
This is a simple test you can do for yourself. Take three to five air-dry ped, each about 3-5 mm, and place in clean water and repeat the test in some greywater from your laundry wash water. The response you get will determine whether you need to (a) do nothing to the soil; (b) ameliorate the soil to overcome the effects of the greywater; or (c) avoid using greywater.
While it is beyond the scope of these pages, the real problems with spreading greywater on gardens comes when it rains rather than when the greywater is being applied. Thus, while ever it remains dry, and we continue to irrigate with greywater we may think there are no problems. Then when the rain comes, and we stop using greywater – be aware! Look for signs of water ponding in areas where it has not ponded before and signs of water stress in the plants. You may need to ameliorate to return the soil to its former status.
Amelioration of irrigation area
Like all good stories, this one is not the dismal outlook that has been portrayed above. There are ways of re-mediating an area that has been ruined by highly saline or highly sodic greywater. There are usually not too many ways that the soil will become unusable because of high phosphorus from greywater irrigation, but sodium is a different matter. Don’t be misled by those who suggest that high phosphorus kills native trees. Other than Banksia species and a few similar species, all natives will respond favourably to additional phosphorus, just the same as lawn and exotic plants respond. Phosphorus is an essential plant nutrient – low phosphorus means slow growth, but salt, not good!
The effect we saw from having high sodium (middle photo above) is really one that has high sodium relative to calcium and magnesium. Therefore, to ameliorate the area, we can add calcium or magnesium salts in the form of agricultural lime (calcium carbonate), gypsum (calcium sulphate) or dolomite (calcium & magnesium carbonate). We do not use hydrated lime (brickie’s lime) because it will dissolve organic material in the soil and elevate the pH to alkaline conditions.
How much lime or gypsum do we use? That’s another answer that depends upon soil type and the effect that sodium will have on the soil. Sandy soils don’t need any because the sodium can be easily leached through the sandy soil with excess greywater or rainfall. Clay soils depend upon the type of clay and the impact that sodium has on the dispersion, but as a guide anything less than about a cup per square metre is simply not enough. Somewhere between one and 3 cups full per square metre will do no harm. Some soils require about four cups per square metre. Simply try a small area at one cup per square metre and see the difference.
We use gypsum where we do not want to elevate the soil pH. Gypsum adds calcium and sulphur to the soil (both plant macro-nutrients) without changing the soil pH but gypsum does change soil salinity. In this case the soil salinity is a benefit because the calcium helps to dislodge the sodium so that it can be leached by rainwater. Lime, however, adds calcium but also increases pH towards being more alkaline, as well as increasing salinity slightly. How much it shifts the pH depends upon the application rate and the soil properties. You will need a lab test to determine the exact amount of lime required.
Dolomite is used in place of lime, or with lime, when you need to add magnesium. Dolomite behaves the same as lime, elevating the pH as well as increasing salinity.
What’s the difference between fertilisers and greywater
The difference may not be very much. The elements in fertilisers are, ideally, soluble in water and the elements in greywater are already dissolved in the water. But the substantial difference is that not many fertilisers have the same proportion of sodium that your greywater is likely to have. Most fertilisers have little sodium because sodium is so detrimental to plants.
Many valuable garden fertilisers (as distinct from superphosphate used on farming lands) have various ratios of nitrogen, phosphorus and potassium (see ratios of N:P:K on the label) because these elements are required in reasonably large amounts and are called macro-nutrients. Sulphur, calcium, and magnesium are also macro-nutrients. Other nutrients are required in minute doses and include zinc, iron, copper, boron, molybdenum. So we can buy fertilisers that have various mixtures of these macro and micro-nutrients, fertilisers to suit roses, vegetables, lawns, orchids and other specific groups of plants.
Unfortunately, the manufacturers of laundry products are not so kind as to put other elements in the laundry products that your plants require. Indeed, many laundry product manufacturers do the exact opposite. They use substantial amounts of sodium that are detrimental to soils and plants. There is almost no nitrogen or potassium in laundry detergents and calcium and magnesium would be detrimental to laundry detergents because they make the water “hard” and block out the effect of the detergents. Therefore, greywater has little of the positive attributes of fertiliser other than the phosphorus and perhaps sulphur (in powders). So, if you choose a detergent that is low in phosphorus, there’s not much other than the water that is beneficial for the plants. And if you choose a laundry detergent that is low in phosphorus and high in sodium, then your garden will start to look sick in a short time.
If you consider that a 50 kg bag of superphosphate (11% P) is worth about R500, then that is equivalent to 15 years’ worth of greywater from a detergent that has 1 g P/wash, so the phosphorus in the detergent is a mighty expensive way of putting phosphorus on your garden. But putting the greywater on the garden is better than discharging the greywater to sewer.
The other consideration is that when you use fertilisers, the N:P:K:S ratio is blended to suit particular plant groups and an ideal ratio for most plants is 100 N : 1P : 1 K and 1S with very low Na. In greywater you are likely to have very low N, a bit of P, almost no K and heaps of Na…….greywater is not a fertiliser and never will be!
Add fertilisers to your greywater irrigation area
Now this may sound like a stupid suggestion because many people think that the components in greywater are plant nutrients. Well, as explained above, there are very few essential plant nutrients in greywater and a substantial amount of detrimental sodium. Most of the benefit you see from using greywater is from the water, not what is in it. Because the extra water is encouraging the plants to grow, then plant nutrients must also be available if the plants are to grow well. You will need to add nitrogen, some more phosphorus, potassium and calcium. A good N:P:K mix from your nursery supplier, or some soluble fertiliser with a small application of gypsum would be wise. On sandy soils, small applications often and on clay soils one or two applications per year. Don’t think that you can get away without additional fertilisers – the plants won’t like you for that behaviour!
This advice is offered in general terms. Your specific requirements will have to be addressed according to the greywater application rate, the climate, soil type and plant species.
feel free in to contact us for an obligation free assessment.