You bought a TDS meter. Maybe someone on a Cabo expat Facebook group recommended it, or you saw a YouTube video about water quality. You filled a glass from the kitchen tap, dipped the meter in, and the screen showed a number that made your stomach drop: 847.
You Googled “TDS 847 safe?” and found a hundred conflicting answers. Some said anything above 500 is dangerous. Others said it doesn’t matter. The WHO document was dense and unhelpful. You’re now more anxious than before you tested.
Here’s what that number means, what it doesn’t mean, and what to actually do about it.
What Hard Water Means in Los Cabos
Water in Los Cabos is hard — typically 600–1,000+ ppm TDS, which is “very hard” by any global classification. This is because the local aquifer runs through limestone geology, dissolving calcium and magnesium carbonates into the water supply. High TDS means high mineral content. It does NOT mean the water is unsafe. The WHO has no health-based guideline for water hardness. Hard water is an aesthetic and economic problem — scale on fixtures, shortened appliance lifespan, soap that doesn’t lather well, stiff laundry, and mineral taste — not a safety crisis. The health risks in Cabo water come from microbial contamination related to storage conditions, not mineral content.
Why Cabo Water Is So Hard
This isn’t a pollution problem. It’s geology.
The Baja California peninsula is largely composed of granite, sandstone, and — critically — limestone. The San José del Cabo aquifer, which supplies the vast majority of the region’s water, sits in a geological formation rich in calcium carbonate. As rainwater percolates through the rock on its way to the aquifer, it dissolves calcium and magnesium from the limestone. By the time it reaches the water table, it’s carrying those minerals in solution.
For context: the U.S. Geological Survey classifies water hardness as follows (measured as mg/L of calcium carbonate):
- Soft: 0–60 mg/L
- Moderately hard: 61–120 mg/L
- Hard: 121–180 mg/L
- Very hard: 180+ mg/L
Most Cabo water registers above 300 mg/L — some areas above 600 mg/L. On the standard hardness scale, Cabo doesn’t just exceed “very hard” — it’s off the chart.
Desalination plants produce soft water (TDS below 100), and as desalinated water increasingly supplements the supply, some properties receiving blended water will see lower TDS over time. But for now, the majority of Cabo water — from OOMSAPAS, from wells, from pipas sourcing from the aquifer — is naturally, irreversibly hard.
This isn’t fixable at the municipal level. You can’t remove geology from the aquifer. You can only treat the water after it arrives.
What TDS Does and Doesn’t Tell You
TDS — Total Dissolved Solids — is the most accessible water metric because the meters are cheap ($15), instant, and require zero training. Dip, read, done. This accessibility makes TDS the default number people share, compare, and worry about.
But TDS is a blunt instrument. It tells you the total concentration of everything dissolved in the water — calcium, magnesium, sodium, sulfate, chloride, bicarbonate, silica, and dozens of other dissolved substances. It does not tell you which substances are present, in what proportions, or whether any of them are harmful.
What a TDS meter tells you: How mineralized your water is. Useful for tracking hardness, comparing sources (OOMSAPAS vs. well-sourced pipa), and monitoring trends over time. If your TDS jumped 200 ppm between deliveries, your pipa may have changed sources.
What a TDS meter does NOT tell you:
- Whether bacteria are present (microbial contamination has no TDS signature)
- Whether heavy metals are present at concerning levels (these are measured in parts per billion, invisible to a TDS meter)
- Whether the water is “safe” in any health-relevant sense
The most dangerous water in a Cabo cistern — old water with zero chlorine residual and active biofilm — might have the exact same TDS reading as freshly delivered, fully treated municipal water. TDS is a hardness indicator, not a safety indicator. Conflating the two is the single most common water quality mistake expats make.
What Hard Water Actually Does to Your Home
The problems are real — they’re just not the problems most people worry about.
Scale on everything. White or off-white mineral deposits on faucets, showerheads, glass doors, tile, and countertops. This is calcium carbonate precipitating as water evaporates. In Cabo’s dry climate, evaporation is fast, and deposits form aggressively. Cleaning requires acidic solutions (vinegar, citric acid, commercial descaler) — regular soap and water just smear it around.
Appliance destruction. The expensive problem. When hard water is heated, dissolved minerals come out of solution and deposit on heating elements and heat exchangers. Your water heater, dishwasher, washing machine, coffee maker, and any other appliance that heats water accumulates scale internally.
Water heaters take the worst hit. A typical electric or gas water heater in a moderate-hardness city might last 10–15 years. In Cabo, expected water heater lifespan, estimated 3-5 years without treatment, 7-10 years with softening. Source: appliance surveys and plumber interviews. Update annually. is common. The heating element scales over, efficiency drops by 📝 Needs citation: 20-30% with moderate scale buildup. Source: DOE or equivalent., the thermostat compensates by running longer, energy costs rise, and eventually the element burns out or the tank corrodes through.
Plumbing diameter reduction. Over years, scale narrows the interior diameter of copper and galvanized pipes. A ½” pipe becomes effectively ⅜”, then ¼”. Flow drops. Pressure drops. Hot water takes longer to arrive. In severe cases, pipes need replacement — a major plumbing expense that could have been deferred with water treatment.
Laundry and cleaning. Hard water reacts with soap to form soap scum instead of lather. Clothes washed in hard water feel stiff and retain a mineral residue. Detergent consumption increases because you need more product to achieve the same cleaning action. Whites develop a grayish tinge over time.
Hair and skin. Many Cabo residents notice changes in their hair and skin after moving from a soft-water city. Hair feels drier, coarser, and harder to manage. Skin may feel tight or itchy after showering. These effects are cosmetic — not medically dangerous — but they’re the daily quality-of-life impact that makes people most viscerally frustrated with hard water.
What Hard Water Does NOT Do
Hard water does not make you sick.
The WHO’s Guidelines for Drinking Water Quality do not set a health-based guideline for water hardness. At the TDS levels typical in Cabo (600–1,000+ ppm), the dissolved minerals are primarily calcium and magnesium — nutrients your body needs. Some research suggests hard water may provide a modest dietary contribution of these minerals, though the evidence is mixed.
Hard water at Cabo levels:
- Does NOT cause kidney stones (this is a persistent myth with no strong epidemiological support at typical drinking water hardness levels)
- Does NOT cause gastrointestinal illness
- Does NOT indicate bacterial contamination
- Does NOT mean the water is “polluted”
The health risks in Cabo water are microbiological — related to cistern hygiene, chlorine residual, biofilm, and water age. These risks exist independently of hardness. You can have soft, clean water that’s microbiologically unsafe, and hard, mineral-rich water that’s microbiologically safe. The two dimensions don’t correlate.
This distinction matters because it changes what you should worry about and what you should spend money on. If your TDS is 900 but your cistern is clean, recently filled with treated water, and has active chlorine residual — your water is hard but safe. If your TDS is 400 but your cistern hasn’t been cleaned in years and has biofilm on every wall — your water is softer but less safe.
The Hidden Connection
Hard water and the sediment multiplier are partners. Dissolved minerals in hard water don’t just cause scale on appliances — they precipitate inside the cistern, contributing to the sediment layer on the floor. This mineral sediment joins the sand, silt, and organic matter delivered by pipas, creating a composite layer that combines abrasive mineral particles with biologically active organic material.
The mineral precipitation also happens on the walls — not as dramatic as biofilm, but as a thin calcium carbonate film that provides additional surface roughness for biofilm to colonize. Hard water doesn’t cause biofilm, but it creates better conditions for biofilm attachment.
Addressing hard water and addressing sediment are connected interventions. A water softener reduces the mineral load reaching appliances and pipes. Inlet filtration reduces the particulate load reaching the cistern. Cistern cleaning removes the accumulated result of both. The most effective approach addresses all three — but if you can only do one thing, the inlet filter has the broadest impact per dollar.
What You Can Do About Hard Water
The free fix: Accept what you can’t change and focus on what you can. Hard water is geology — you’re not going to soften the aquifer. But you can reduce the damage: use vinegar or citric acid to clean scale from fixtures weekly (prevents buildup from becoming permanent). Wipe glass shower doors after each use. Run your dishwasher with a rinse aid. Lower your water heater temperature to 50°C — lower temperatures produce less scale.
The cheap fix ($50–150): Install a polyphosphate scale inhibitor on the cold water inlet to your water heater. These cartridge-based systems dose a small amount of food-grade polyphosphate into the water, which prevents calcium carbonate from crystallizing on heating surfaces. They don’t soften the water (your TDS won’t change), but they significantly reduce scale formation in heated appliances. Cartridge replacement every 6 months costs replacement cartridge cost, expected $200-500 MXN. Source: local supplier survey..
The right fix ($500–2,500 USD): A whole-house water softener using ion exchange. These systems replace calcium and magnesium with sodium, producing genuinely soft water throughout the house. Benefits: no scale on any surface, better lather, softer laundry, dramatically extended appliance life, eliminated fixture cleaning. Drawbacks: initial cost, ongoing salt refills (salt cost, expected $200-400 MXN/month. Source: supplier survey.), slightly elevated sodium in the water (not suitable for very low-sodium diets), and the softened water has a different “feel” that some people dislike.
For drinking water specifically, a point-of-use reverse osmosis system removes minerals, bacteria, and dissolved contaminants in one step — producing water with TDS below 50 ppm. This is the alternative to buying garrafones and the most cost-effective long-term approach to drinking water quality.
The Cost of Doing Nothing
Hard water damage is the ultimate slow drain. No single month’s impact is dramatic enough to trigger action. But compounded over years:
Water heater: Replacement every 3-5 years without treatment at $8,000–15,000 MXN each, instead of every 10–15 years with treatment. Extra cost over 10 years: expected $15,000-30,000 MXN in accelerated replacements.
Energy: Scaled heating elements consume 📝 Needs citation: 20-30% more energy for the same heat output. On a typical Cabo electricity bill, that’s estimated monthly energy waste, expected $200-500 MXN/month.
Plumbing: Pipe rescaling or replacement is a major intervention at expected $10,000-30,000 MXN depending on scope. Not every home reaches this point, but those with the hardest water and longest residence do.
Cleaning supplies and time: The hours spent scrubbing mineral deposits off glass, tile, and fixtures — quantifiable if you value your time, which you should.
Cosmetics: Higher shampoo and conditioner consumption, potential purchase of shower filters or specialty hair products.
Total estimated cost of untreated hard water in a Cabo home: expected $15,000-40,000 MXN/year when all factors are included. Source: lifecycle analysis. Update annually.. A water softener’s annual operating cost is roughly expected $5,000-10,000 MXN/year including salt and maintenance. The math favors treatment in most cases.
Frequently Asked Questions
Is 800 TDS dangerous? ¿Es peligroso un TDS de 800? No. TDS of 800 ppm indicates very hard water — high in dissolved minerals, primarily calcium and magnesium. The WHO does not set a health-based guideline for TDS. At 800 ppm, you’ll experience significant scale buildup on appliances and fixtures, soap that doesn’t lather well, and mineral taste. But it’s not a health risk. The health risks in Cabo water come from microbial contamination, not mineral content, and those risks are not measurable with a TDS meter.
Should I install a water softener? ¿Debería instalar un suavizador de agua? If you plan to stay in your property for more than 2–3 years, a whole-house water softener typically pays for itself in extended appliance life and reduced maintenance. The decision depends on your water hardness (test it), your budget, and your tolerance for the ongoing cost of salt refills. For shorter stays or rental properties, a polyphosphate scale inhibitor on the water heater is a more cost-effective partial solution.
Does boiling remove hardness? ¿Hervir el agua elimina la dureza? Partially. Boiling removes “temporary hardness” (calcium bicarbonate) by converting it to calcium carbonate that precipitates out — this is the white residue in your kettle. But it does not remove “permanent hardness” (calcium sulfate and magnesium compounds). In Cabo, a significant portion of the hardness is permanent, so boiling has limited effect on total hardness. It also concentrates any remaining minerals.
Why does my TDS change between pipa deliveries? ¿Por qué cambia mi TDS entre entregas de pipa? Because the source water may differ between deliveries. If your pipa switches from an OOMSAPAS hydrant (lower TDS, treated water) to a private well (higher TDS, untreated), you’ll see a measurable jump. Conversely, if your area starts receiving more desalinated water blended into municipal supply, TDS may drop. Tracking TDS over time gives you a rough proxy for source consistency — a sudden change warrants a conversation with your pipa provider.
Is desalinated water better? ¿Es mejor el agua desalinizada? Desalinated water is much softer (TDS typically under 100 ppm after remineralization) and microbiologically clean. If your water supply increasingly includes desalinated water, your hardness problems will diminish. However, most Cabo residents don’t receive pure desalinated water — it’s blended with aquifer water in the municipal distribution system. The blended TDS depends on the ratio, which varies by location and demand.
Related Reading
Worried about safety, not just hardness? They’re different questions with different answers: Is Cabo Water Safe?
Want to understand the full damage cascade? Minerals are one component of a bigger problem: The Sediment Multiplier
Ready to test your water properly? Beyond the TDS meter: Testing Your Water
Looking at treatment options? The complete decision framework: Filtration Guide
Want to know what all this costs over time? The economics of Cabo water: Costs Overview
Understand Your Water
Hard water is a daily reality in Los Cabos — but how hard, and what it’s costing you, depends on your specific property and source. The Water Health Diagnostic assesses your hardness level, estimates your annual damage cost, and recommends treatment options matched to your budget and situation.