Borehole water is not automatically good water. Plenty of Cape Town households drilled after the Day Zero years, connected the pump to the irrigation system, and then watched the lawn go patchy, the paving turn orange and the beds slowly decline — while watering more than ever.
Two things are usually behind it: salinity, which burns roots and thins the lawn, and dissolved iron, which oxidises on contact with air and stains everything it touches. Both are manageable, but only once you know which one you have.
Get the water tested before you diagnose anything
Everything below depends on numbers you do not currently have. A basic irrigation water analysis from a laboratory is inexpensive relative to a lawn, and it tells you what you are actually dealing with. Ask for:
- Electrical conductivity (EC) or total dissolved solids — the overall salinity measure.
- Sodium, chloride and the sodium adsorption ratio (SAR) — sodium is the specific troublemaker for both plants and soil structure.
- Iron and manganese — the staining culprits.
- pH and hardness (calcium, magnesium) — affects nutrient availability and scaling.
Boreholes near the coast — Milnerton, Table View, Blouberg, Melkbosstrand and the Strand side — are more likely to show elevated sodium and chloride, because coastal aquifers sit close to a saline interface and can draw seawater in when over-pumped. Inland Northern Suburbs boreholes more often show iron. That is a tendency, not a rule; test yours.
What salty water does to a lawn
Salinity harms grass in two separate ways, and they need different fixes.
Osmotic stress. High dissolved salt in the soil water makes it physically harder for roots to take up water. The lawn shows classic drought symptoms — dulling, blue-grey cast, slow recovery from footprints, thinning — while the soil is wet. Watering more makes it worse, because you are adding more salt.
Sodium toxicity and soil damage. Sodium specifically displaces calcium on soil particles, which destroys structure in clay-rich soils. Durbanville and the heavier eastern Northern Suburbs soils are vulnerable: they crust, seal over and stop infiltrating. Then water ponds on the surface while the root zone stays dry. On Cape Flats sand the structural damage is less, but salt accumulates in the root zone anyway during our dry summers because there is no rain to flush it.
Symptoms worth recognising: browning that starts at leaf tips and edges; a white crust on soil or the edges of beds; damage worst furthest from the sprinkler where fine spray evaporates and concentrates; and salt-sensitive plants dying while tough ones nearby look fine.
What iron-rich water does
Iron in groundwater is dissolved and colourless underground. The moment it hits air it oxidises to iron oxide — rust — and deposits as an orange-brown film.
You see it on paving, boundary walls, plaster, pool coping and the sides of light-coloured houses wherever a sprinkler throws spray. It is not dirt. Scrubbing does little and pressure washing usually just spreads a thinner version of the same stain. Iron also blocks drippers and micro-sprayers, which is why iron-water irrigation systems clog constantly.
Iron is generally not toxic to lawn at typical borehole concentrations. It is a cosmetic and maintenance problem, not a plant health one — but a serious one when your new driveway turns orange in a season.
Fixing the irrigation side first
Before you change plants or treat water, change how you water. Several problems are layout problems.
- Keep spray off hard surfaces. Re-aim or replace sprinklers so nothing lands on paving, plaster or walls. This alone eliminates most iron staining. Use adjustable-arc heads at bed edges.
- Water deeply and less often. Deep, infrequent irrigation pushes salts down past the root zone. Frequent light watering concentrates them exactly where the roots are. This is the single most important change on saline water.
- Switch to drip or subsurface delivery in beds. Water goes into the soil rather than onto foliage, which stops leaf burn from salty spray. Fit good filtration and plan on flushing lines if you have iron.
- Water early morning. Less evaporation means less salt concentrating at the surface, and foliage dries before the heat.
- Let winter rain do the flushing. Cape Town’s winter rainfall is a genuine advantage here. Rain leaches accumulated salt out of the root zone every year, which is why saline-irrigated lawns often recover in spring. Do not irrigate over winter with borehole water and cancel out the flush.
Treatment options, honestly assessed
| Problem | Option | Verdict |
|---|---|---|
| Iron staining | Aeration and settling tank | Effective and low-tech — oxidise the iron in a tank, let it settle, irrigate off the top |
| Iron staining | Oxidising filter system | Works well; ongoing maintenance and backwash requirement |
| Iron in drippers | Filtration plus line flushing | Necessary if you keep drip on iron water |
| Salinity | Blending with municipal or rainwater | The most practical dilution route where you have both |
| Salinity | Reverse osmosis | Genuinely removes salt, but the cost and the reject water make it hard to justify for a garden |
| Sodium-damaged soil | Gypsum application | Well-established fix — calcium displaces sodium so rain can leach it out |
| All of it | Change what you grow | Usually the cheapest and most durable answer |
“Magnetic” and similar conditioning devices sold for borehole water do not remove salt or iron. Be sceptical.
What survives saline irrigation
Grass species differ enormously in salt tolerance, and this is where you can solve the problem by choosing correctly rather than treating water forever.
- Buffalo grass and paspalum types are at the tolerant end and cope with moderately saline irrigation.
- Kikuyu sits in the middle. It is what most Cape Town lawns are, and it will survive mild salinity while looking thinner than it should.
- Fine fescues and cool-season blends are the least tolerant and are the wrong choice on borehole water.
For beds, coastal and fynbos species are the obvious answer — they evolved in saline, nutrient-poor, sandy conditions. Wild rosemary, bietou, restios, sour fig, num-num, aloes, agapanthus and tulbaghia all shrug off water that kills soft exotics. Our fynbos garden ideas guide covers the full palette, and the same species list applies inland if your water is the problem rather than the air.
Conversely: hydrangeas, azaleas, most soft-leaved ornamentals and anything requiring rich moist soil will fail on saline water regardless of how much you fuss over them.
When artificial grass is the rational answer
If your borehole is saline, your soil is heavy, and you are pouring water and gypsum at a lawn that never quite looks right — the honest answer may be to stop growing grass there.
Artificial grass is unaffected by salinity, and it removes the largest single water demand in most gardens. It is not free: quality artificial grass runs R380 – R650 per m² supplied and installed, against R80 – R140 per m² for instant kikuyu laid. Over ten years, though, the totals cross — largely because of water and maintenance. Our artificial grass vs real lawn comparison works through the ten-year numbers, and our artificial lawn installation service covers the base build-up.
One warning specific to iron water: do not irrigate artificial grass with iron-rich borehole water to “cool it down”. You will stain it, and unlike paving you cannot acid-treat it.
Dealing with iron stains already on your paving
Iron oxide staining on paving does not respond to ordinary cleaning. It needs a purpose-made rust or iron stain remover, usually oxalic acid based, applied to a damp surface, left to dwell and rinsed thoroughly — and always tested on a hidden brick first, because these products can lighten pigmented concrete pavers.
Do not reach for hydrochloric acid. It etches the surface, damages joints and often leaves the paving looking worse than the stain did. Re-sand the joints after any treatment.
Crucially: remove the stain and fix the sprinkler that caused it, or you will be doing this every year.
A sensible order of operations
- Test the water. EC, sodium, chloride, iron, pH.
- Re-aim every sprinkler so nothing hits a hard surface.
- Move to deep, infrequent irrigation; stop borehole watering through the wet winter months.
- If sodium is high and your soil is heavy, apply gypsum and let winter rain leach it.
- If iron is the issue, add an aeration and settling tank before the irrigation line.
- Re-plant the worst areas with tolerant species, or convert lawn you do not use.
- Clean existing iron staining last, once the cause is fixed.
If you want the garden side of that handled — irrigation layout, planting changes, paving cleaning or a turf decision — our landscaping and gardening team works across Cape Town, and you can send us your water test results along with a few photos.
Quick answers
Can borehole water kill my lawn?
Saline borehole water can. High sodium and chloride cause tip and edge burn, thinning and drought-like symptoms even in wet soil, and sodium damages structure in clay soils. Test EC, sodium and chloride before assuming it is a watering problem.
Why is my paving turning orange from the sprinklers?
Dissolved iron in the borehole water oxidises to rust when it hits air and deposits on paving, walls and plaster. Re-aim the sprinklers off hard surfaces, and treat existing marks with an oxalic-acid based iron stain remover — never hydrochloric acid.
Which lawn handles borehole water best in Cape Town?
Buffalo grass and paspalum types are the most salt tolerant. Kikuyu is moderately tolerant and will survive mild salinity looking thinner than it should. Fine fescue blends are the worst choice on saline water.