The most effective way to lower total dissolved solids (TDS) in water is reverse osmosis, which removes 90–99% of dissolved minerals, salts, and organic matter. Other options include distillation and deionization, each with different costs and tradeoffs. The right method depends on your starting TDS level, how much water you need to treat, and what you plan to use it for.
What TDS Actually Measures
TDS is the sum of everything dissolved in your water: calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, nitrate, and silica make up the bulk of it. These ions come from natural rock and soil, agricultural runoff, water treatment chemicals, and aging pipes. A handheld TDS meter doesn’t identify which minerals are present. It measures electrical conductivity (how well ions carry a current between two electrodes) and converts that reading to parts per million (ppm) using a conversion factor of roughly 0.5.
The EPA sets a secondary guideline of 500 ppm for TDS in drinking water. This isn’t a legally enforced limit. It’s an aesthetic standard, meaning water above 500 ppm is generally safe but may taste salty, metallic, or bitter, and can look cloudy. Most municipal tap water falls between 200 and 400 ppm. Well water can range from under 100 ppm to well over 1,000 ppm depending on local geology.
Why High TDS Causes Problems
Taste is the most immediate issue. Water above 500 ppm often has a noticeable mineral flavor that makes it unpleasant to drink and can affect the taste of coffee, tea, and cooked food. But the practical damage shows up in your home over time.
Scale from dissolved calcium and magnesium builds up on water heater elements and tank walls, acting as insulation that forces the heater to work harder. The result is higher energy bills, longer heating times, and an increased risk of tank failure. Dishwashers develop clogged spray arms and coated heating elements, leaving cloudy glassware and white residue on dishes. Washing machines suffer from mineral deposits on internal valves and hoses, and detergents dissolve poorly in high-TDS water, leaving clothes stiff, faded, or dingy. Appliances exposed to untreated high-TDS water often fail years earlier than expected, and this damage begins from day one, even in brand-new homes.
Reverse Osmosis (Best for Drinking Water)
Reverse osmosis (RO) pushes water through a semipermeable membrane with pores small enough to block dissolved ions. A typical under-sink RO system brings tap water from 300–500 ppm down to 10–50 ppm. Most residential units produce 50–100 gallons per day and cost $150–$400 upfront, with replacement filters and membranes running $50–$100 per year.
RO systems do produce wastewater. For every gallon of purified water, older systems send 3–4 gallons down the drain. Newer models with permeate pumps improve this to roughly a 1:1 ratio. The membrane typically lasts 2–3 years, while the pre-filters (sediment and carbon) need replacement every 6–12 months to protect the membrane from chlorine damage and clogging.
For whole-house treatment, RO systems scale up significantly in size and cost, often $1,500 and above plus professional installation. Most people opt for a point-of-use system at the kitchen sink instead.
Distillation
Distillation boils water into steam and then condenses it back into liquid, leaving dissolved solids behind. It removes virtually all TDS, often producing water below 5 ppm. Countertop distillers cost $100–$300 and process about one gallon every 4–6 hours, using roughly 3 kilowatt-hours of electricity per gallon. That makes distillation effective but slow and energy-intensive. It works well if you only need a few gallons of very pure water per day, but it’s impractical for higher volumes.
Deionization
Deionization (DI) uses two types of resin to strip ions from water. One resin swaps hydrogen for positively charged minerals like calcium, magnesium, and sodium. The other swaps hydroxide for negatively charged ions like chloride, sulfate, and nitrate. The released hydrogen and hydroxide combine to form pure water. Mixed-bed DI cartridges can produce extremely pure water, suitable for aquariums, laboratory work, and automotive detailing.
The catch is that DI resin exhausts quickly when treating tap water with moderate to high TDS. A small cartridge might last only 50–100 gallons on municipal water. That’s why DI is most commonly used as a polishing step after RO, where it can last hundreds or even thousands of gallons because the RO membrane has already removed the vast majority of dissolved solids. Standalone DI is cost-effective only for small volumes of very pure water.
Water Softeners Lower Hardness, Not TDS
A common misconception is that a water softener will reduce TDS. Traditional salt-based softeners swap calcium and magnesium ions for sodium ions. This eliminates scale buildup and improves soap performance, but the total dissolved solids remain roughly the same because you’re replacing one set of ions with another. If your concern is specifically TDS (taste, for example), a softener alone won’t solve it. If your concern is scale damage to appliances and pipes, a softener is the right tool and often more practical than whole-house RO.
Activated Carbon Filters
Standard carbon filters, including pitcher filters and refrigerator filters, are designed to remove chlorine, volatile organic compounds, and some pesticides. They do very little to reduce TDS because dissolved mineral ions pass right through the carbon. If you test your water before and after a carbon filter, you’ll see almost no change in the TDS reading. These filters improve taste by removing chlorine, which is why people sometimes assume TDS has dropped, but the minerals remain.
How to Test Your Water
A handheld TDS meter costs $10–$25 and gives you an instant reading. Dip the electrodes into a water sample, and the screen displays ppm. These meters are factory-calibrated (commonly at 342 ppm) and stay consistent for general use, though recalibration with a standard solution is a good idea after prolonged use. Keep in mind that even very pure water may read 1–2 ppm on a meter due to carbon dioxide from the air dissolving into the sample.
For a full picture of what’s in your water, a lab test is more useful than a TDS meter alone. Since TDS meters can’t distinguish between harmless calcium and potentially concerning nitrate or lead, a lab panel tells you exactly which dissolved solids are elevated. Many county health departments offer free or low-cost well water testing, and private lab kits typically run $30–$150.
Adding Minerals Back After Treatment
If you use RO or distillation, your water will have very low mineral content. Water below about 50 ppm tastes flat to many people, and there is some evidence that long-term consumption of very low mineral water may reduce the dietary intake of calcium and magnesium that would otherwise come from drinking water. The simplest ways to remineralize treated water are a mineral filter cartridge added to your RO system (many manufacturers sell these as an add-on stage), an alkaline water pitcher with a mineral filter, or liquid trace mineral drops added directly to your glass or pitcher. These methods typically bring TDS back up to 30–80 ppm, enough to improve taste without reintroducing the problems you filtered out.
Choosing the Right Method
- For drinking and cooking water under 1,000 ppm TDS: An under-sink RO system is the most practical and cost-effective solution for most households.
- For very high TDS well water (above 1,000 ppm): A whole-house RO system or a combination of softener plus point-of-use RO handles both appliance protection and drinking water quality.
- For small volumes of ultra-pure water: Distillation or an RO-plus-DI setup works well for aquariums, humidifiers, or specialty uses.
- For scale prevention only: A water softener addresses the appliance damage without changing TDS, which is sufficient if taste isn’t your concern.