Water
How a greywater system works and what the law requires
Reusing bath, basin, and laundry water is one of the quickest ways to cut municipal consumption — but the biology and the by-laws both have teeth. Here is what you need to understand before you connect anything.
The short answer
A greywater system collects water from baths, basins, showers, and laundry, then routes it to the garden or to a treatment stage before reuse. South African law requires that stored greywater be used within 24 hours, that it never surface-pond, and that any system beyond a direct-to-garden diverter is approved by your municipality under SANS 10252. The sodium content of most local detergents means soil conditioning is not optional — it is part of making the system work.
What counts as greywater and what does not
Greywater is waste water from baths, showers, hand basins, and laundry machines — water that has been used but carries no faecal contamination. It is distinct from blackwater, which is any water that has contacted a toilet, and from kitchen water, which the regulations treat as a separate and harder category.
Kitchen sink and dishwasher water occupies a grey area that most South African municipalities push toward blackwater treatment. The fat, food solids, and pathogen load from raw-meat preparation make it substantially more hazardous than bath or laundry water. Unless your municipal by-law explicitly permits kitchen greywater reuse, treat it as blackwater and route it to the sewer.
Toilet cistern water, condensate from air conditioners, and water softener backwash are not greywater in the legal sense and each carries its own requirements. Stick to the four sources — bath, shower, basin, laundry — and you are working in well-established territory.
| Source | Greywater? | Notes |
|---|---|---|
| Bath and shower | Yes | Standard greywater source |
| Hand basins | Yes | Standard greywater source |
| Laundry machine | Yes | Sodium content requires management — see below |
| Kitchen sink | No (typically) | Fat and food solids push this toward blackwater treatment |
| Dishwasher | No (typically) | High-temperature water with enzyme-heavy detergent |
| Toilet | No | Blackwater — never |
| AC condensate | No | Not greywater; usually permissible to reuse separately |
The 24-hour rule and the biology behind it
SANS 10252-2 and the National Building Regulations require that greywater stored in any vessel be used within 24 hours of collection. This is not an arbitrary bureaucratic figure. It reflects the growth curve of the pathogens that greywater carries — E. coli, Salmonella, and skin-borne bacteria — in a warm, nutrient-rich liquid. Within 24 hours, bacterial load is manageable. After 48 hours, greywater in a closed tank begins to ferment and smell; after 72 hours, it is microbiologically similar to dilute sewage.
South African conditions accelerate this curve. Ambient temperatures in most of the country are significantly higher than the temperate climates where much international greywater guidance was written. A tank sitting in the sun at 32°C will approach the 48-hour threshold in far less than 48 hours. Insulate the tank or shade it, and design the system so that the 24-hour volume matches your actual daily irrigation demand — not your aspirational one.
The rule also has a surface-ponding corollary: greywater may never pool on the surface. It must be discharged below mulch, into a subsurface irrigation line, or directly onto plant root zones in a way that absorbs immediately. Surface pooling creates a vector for human contact and for mosquito breeding, both of which your municipality will regard as a public health matter.
Three system types: how each one works
The choice of system is not primarily aesthetic. It follows from how much water you generate, how quickly you can use it, and whether your local authority requires approval.
Direct-to-garden diverter
The simplest configuration: a valve or a branched fitting in the outlet pipe of a bath or shower routes water directly to a subsurface irrigation line or a mulched garden bed rather than to the sewer. There is no storage, no pump in most installations, and no treatment. Because there is no storage, the 24-hour rule is trivially satisfied — water goes straight into the soil.
The limitations are equally simple. You can only irrigate when someone is bathing. You cannot build up a reserve for a dry day. And the garden zone must be lower than the outlet, or you need a small pump. For a household that bathes in the morning and wants to water in the evening, this system is not sufficient on its own.
Surge tank system
A surge tank — typically 100 to 500 litres — sits between the household outlets and the garden. Water drains into the tank throughout the day and is released to irrigation by a timer, a float valve, or a small pump. The tank gives you a buffer, which means you can irrigate at a sensible time rather than immediately after each bath.
The 24-hour rule bites here. The tank must be emptied and the contents used within 24 hours of the oldest water entering it. In practice, this means sizing the tank to your actual daily greywater production — not significantly larger. An oversized tank is not a bigger reserve; it is a vessel that will consistently violate the storage rule and begin producing odour.
Most municipalities require approval for a surge tank system. The threshold is typically any system that stores greywater, regardless of volume. Check your local by-law before installing — the approval process varies but generally involves a plumber's certificate of compliance and a site inspection.
Treated greywater systems
A treated system passes greywater through a filtration and disinfection stage — typically coarse filtration, a biofilter, and UV or chlorine disinfection — before storage or reuse. Treated water can be stored longer, used in a toilet cistern, or applied via above-ground irrigation without the same risk profile as raw greywater.
Treated systems require formal municipal approval in virtually all South African metros. The treatment standard is defined in SANS 10252-2 and the National Water Act 36 of 1998. If you intend to reuse treated greywater inside the house — for toilet flushing, for example — you are dealing with a greywater recycling system, and the regulatory bar is meaningfully higher.
Why greywater is different in South Africa
Sodium and boron: what they do to your soil
The sodium problem is specific enough to warrant its own section. Laundry detergents sold in South Africa — particularly powder detergents and cheaper liquid formulations — contain sodium-based builders and softeners. When this water is applied repeatedly to the same soil, sodium ions displace the calcium and magnesium that hold clay particles in aggregates. The soil becomes compacted, hydrophobic, and eventually develops a hard crust that sheds rather than absorbs water.
The measure to watch is the Sodium Adsorption Ratio (SAR) of your irrigation water. Greywater from a laundry-heavy household can have an SAR that, over months of repeated application, pushes even reasonable soils into structural damage. The counter-measure is gypsum (calcium sulphate), applied to the irrigated area at intervals. Gypsum replaces sodium in the soil with calcium, restoring structure without raising soil pH. It is available at most agricultural suppliers and garden centres.
Boron is a second concern. It is present in many dishwasher tablets and some laundry products as a bleach activator. Boron is a micronutrient that plants need in very small quantities — and is toxic in only slightly larger ones. Beans, stone fruit, and most vegetables are sensitive. If your greywater comes primarily from a laundry machine that uses boron-containing detergent, rotate your irrigation zones and let affected soil rest. Dilution with rainwater or borehole water helps.
The practical response is to change what you pour into your machines. Low-sodium, low-boron detergents exist in the South African market — look for formulations marketed as "eco" or "greywater safe". They are not always cheaper, but the soil remediation cost of not using them is real.
| Ingredient | Effect on soil | Risk level | What to do |
|---|---|---|---|
| Sodium-based builders (sodium carbonate, sodium tripolyphosphate) | Disrupts clay structure over time; causes compaction | High with repeated use | Switch to low-sodium formulation; apply gypsum periodically |
| Boron / borax / sodium perborate | Toxic to sensitive plants above low threshold | Medium to high for vegetables and stone fruit | Rotate irrigation zones; dilute with clean water |
| Phosphates | Promotes algae in waterways; less harmful to soil directly | Low for soil; moderate for runoff | Avoid systems that discharge to stormwater |
| Surfactants (biodegradable) | Break down quickly in soil; low residual | Low | Standard risk; no special action required |
| Bleach / chlorine | Kills soil organisms; harmful to roots | High | Do not use bleach-washed water in greywater system |
Which plants and soils tolerate greywater
Sodium tolerance varies widely between plant families. Established trees — particularly indigenous species adapted to seasonal dry conditions — tolerate greywater irrigation well. Lawns are moderately tolerant. Brassicas (cabbage, broccoli, kale) and root vegetables (carrots, beetroot) are sensitive to both sodium and boron and should not receive undiluted laundry greywater.
Sandy soils drain quickly and are less vulnerable to sodium accumulation because sodium ions move through rather than binding to clay particles. Clay soils are most vulnerable and will show damage soonest. Loam soils sit in the middle. If your soil is heavy clay, restrict greywater to mulched tree circles rather than vegetable beds, and apply gypsum at the start of each season.
Fruit trees, ornamental shrubs, and established indigenous plantings are the best recipients of a greywater system in most South African gardens. If the system produces more water than these can absorb in 24 hours, the design needs to be smaller — not the storage tank larger.
Municipal approvals: what is actually required
The National Building Regulations and Building Standards Act 103 of 1977, read with SANS 10252-2, sets the baseline. Any plumbing work that alters the drainage configuration of a building requires a certificate of compliance from a registered plumber. A greywater diverter valve fitted to an existing outlet is a plumbing alteration. The certificate is not optional.
Beyond the certificate, the requirement for formal approval depends on system type and your municipality's by-law. The general pattern across South African metros is:
- Direct-to-garden diverter: plumber's certificate of compliance required; no separate municipal approval in most metros if the system meets SANS 10252-2 criteria.
- Surge tank system (any size): approval required in most metros. Submit to your municipality's water and sanitation department. The City of Cape Town, for example, requires a completed application with a site plan and a plumber's certificate before installation.
- Treated greywater system: formal approval required everywhere. If the treated water is used inside the house (toilet flushing, washing machine reuse), the approval process is more detailed and may require a water use licence under the National Water Act 36 of 1998 depending on volumes.
- Any connection to irrigation that might reach a watercourse or stormwater drain: requires a general authorisation or licence under the National Water Act regardless of system type.
Do not assume that because a neighbour has a system, yours will be approved on the same terms. By-laws are updated, approval thresholds shift, and inspectors apply discretion. The consequence of installing without approval is not only a fine — it is a compliance order to remove the system at your cost.
Contact your local municipality's water and sanitation department before any installation beyond a direct diverter. Ask specifically: what approval is required for a surge tank system, who processes it, what documents are needed, and what the turnaround is. Write down the name of the person you spoke to. This is not excessive caution — it is the difference between a legal installation and an expensive retrofit.
What goes wrong
The most common failure mode is oversizing. A 2,000-litre tank connected to a three-person household's laundry and bathing output sounds like abundance. In practice, it means the tank is rarely more than a quarter full, the water that is in it sits for longer than 24 hours, and within a few weeks the system smells badly enough to be abandoned. Size to actual daily production, not to theoretical maximum.
The second failure is detergent inertia — installing the plumbing correctly but continuing to use the same high-sodium powder detergent. The garden deteriorates over six to eighteen months in a way that is not obviously connected to the irrigation water, and the system gets blamed for poor plant health rather than the chemistry.
Gravity assumptions cause installations that do not drain. A surge tank must be lower than all the outlets feeding it, and the irrigation zone must be lower than the tank outlet, or a pump is required. Measuring fall before laying pipe is not optional.
Blocked filters are the maintenance failure. A coarse filter on the inlet — to catch hair and lint — will block within weeks if not cleaned. A blocked filter causes the system to back up into the house drainage or to overflow. Clean the filter every two weeks as a minimum.
Finally, systems installed without approval are sometimes discovered during a property sale. A conveyancing process that surfaces an unapproved plumbing alteration can delay transfer or require removal. The cost of retrospective approval — if it is even possible — is higher than the original process.
What we would do differently
- Start with a direct diverter on one bath or shower outlet before committing to a tank system. Live with it for a season, observe where the water goes, and measure how much you actually produce versus how much the chosen garden zone absorbs in a day.
- Switch detergents before switching the plumbing. Laundry powder with low sodium and no boron is available; make this change first and give it two or three wash cycles before the first greywater touches a food bed.
- Contact your municipality before buying any tank or pump. The approval process in your specific metro will shape the design — not the other way around.
- Fit a ball valve on the diverter so you can route water to the sewer during illness in the household, when greywater pathogen load is meaningfully higher than normal. This is a SANS 10252-2 requirement, not a suggestion.
- Apply gypsum to the irrigated area at the start of the season — even if you have switched detergents, residual sodium from the first months of use will be working against soil structure.
- Design the storage volume to match daily production, not daily aspiration. Then size the pump (if any) to empty the tank within two hours, so that a load-shedding event during the day does not push you past the 24-hour window.
- Keep a record: the plumber's certificate, the municipal approval reference, and the date of installation. A greywater system is a plumbing alteration that affects property value and transfer — document it accordingly.
Is it worth it?
For most South African households subject to water restrictions, yes — with conditions. A direct diverter on a bath or shower is low-cost, low-complexity, and legal with a certificate of compliance. If it keeps a vegetable garden alive through a Level 3 restriction period, the value is obvious and does not require a financial calculation.
A surge tank system requires more upfront work — approval, a plumber, the tank, and potentially a pump — and ongoing maintenance. It is worth it if your greywater volume matches a genuine daily irrigation need and you are prepared to manage the chemistry. It is not worth it if the system will sit unused half the year, accumulating risk in the form of stale water and blocked filters.
Treated systems are worth it in specific circumstances: households that generate large greywater volumes, properties with no municipal water backup, or installations where toilet flushing reuse would make a meaningful difference to consumption. Outside those cases, the regulatory complexity and maintenance demand of a treatment system exceeds the return for most residential users.
What greywater reuse is not: a solution to water scarcity by itself. A three-person household generates roughly 150 to 250 litres of greywater per day from bath, shower, and laundry combined. That is meaningful — it can sustain a substantial food garden — but it does not replace a functional rainwater tank or a borehole for total water independence. It sits correctly as one layer in a broader water strategy, not as the strategy itself.