The Complete Austin
Water Treatment Glossary.

The adhesion of molecules (gases, liquids, or dissolved solids) to the surface of a material — as opposed to absorption, where molecules penetrate a material's bulk. Adsorption is the core mechanism of activated carbon and KDF media filtration. Contaminants are attracted to and held on the filter media surface rather than passing through. Adsorption capacity is finite — eventually the media surface saturates and must be replaced or regenerated.

A chemical additive — typically a phosphonate or polyacrylate — injected into water to prevent scale formation on pipes, membranes, and heating elements. Antiscalants work by interfering with mineral crystal growth rather than removing minerals from water. Commonly used in commercial RO systems as a pre-treatment to extend membrane life. Not to be confused with water softeners, which physically remove hardness minerals via ion exchange.

The capacity of water to neutralize acids — often called the water's "buffering capacity." Measured in mg/L as calcium carbonate (CaCO₃). Alkalinity is primarily controlled by bicarbonate, carbonate, and hydroxide ions. High alkalinity (>200 mg/L) is common in hard water areas and indicates significant dissolved carbonate minerals. It's distinct from pH — water can have high alkalinity but near-neutral pH. Austin tap water typically runs 150–250 mg/L alkalinity due to Hill Country limestone geology.

A self-cleaning cycle in which water is temporarily reversed through a filter bed to flush accumulated sediment, iron particles, and loosened contaminants out of the system and down the drain. Most whole-house filters and water softeners backwash automatically on a timed or demand-based schedule. During backwashing, filtered water is temporarily unavailable. A typical backwash uses 30–50 gallons and lasts 8–12 minutes. Proper backwash frequency extends media life significantly — under-backwashing leads to channeling and media compaction.

The salt storage reservoir in a salt-based water softener — a separate tank (usually white, 15–18 inches in diameter) that holds sodium chloride or potassium chloride pellets. During the softener's regeneration cycle, water fills the brine tank, dissolves the salt to create a concentrated brine solution, then flushes this brine through the resin tank to recharge the ion-exchange resin. Most brine tanks hold 200–400 lbs of salt and require refilling every 6–12 weeks for a family of four, depending on hardness level and water usage.

A structured community of microorganisms adhered to a surface and encased in a self-produced protective matrix of polysaccharides, proteins, and DNA. Biofilm can form inside pipes, filters, and storage tanks — creating a "slime" layer that harbors bacteria, can harbor pathogens, and reduces water flow. Biofilm is highly resistant to disinfectants — up to 1,000× more resistant than free-floating bacteria. UV disinfection systems help prevent biofilm regrowth in distribution lines. Chloramine disinfection (used in Austin) was partly adopted because it persists longer in the distribution system, helping control biofilm compared to plain chlorine.

A filter made from activated carbon powder compressed into a solid block. Denser than granular activated carbon (GAC) filters, carbon block filters have a smaller pore size (typically 0.5–5 microns) which allows them to remove not just dissolved chemicals but also some particulates, cysts (Cryptosporidium, Giardia), and heavy metals like lead. Commonly used as the second or third stage in under-sink and RO systems. Must be replaced every 6–12 months — when saturated, they can release adsorbed contaminants back into water.

An enhanced form of activated carbon that has been surface-modified — typically through high-temperature steam treatment — to create catalytic reaction sites on its surface. These sites enable chloramine decomposition (through catalysis rather than pure adsorption), as well as effective removal of hydrogen sulfide, iron, and manganese. Catalytic carbon is more expensive than standard GAC but far more effective for Austin's chloramine-treated water. Most premium whole-house filter systems use catalytic carbon as their primary media.

Any physical, chemical, biological, or radiological substance in water other than H₂O molecules. The EPA regulates over 90 contaminants under the Safe Drinking Water Act and sets Maximum Contaminant Levels (MCLs). Contaminants are classed as: primary (health-based: lead, arsenic, nitrates, pathogens, disinfection byproducts) or secondary (aesthetic: hardness, iron, hydrogen sulfide, taste/odor compounds). A substance that exceeds its MCL is a regulated contaminant even if it occurs naturally — arsenic and radium both occur naturally in Texas aquifers. The EWG Tap Water Database lists 42 detected contaminants in Austin's 2025 supply (down from the state average of 56).

A dormant, protective stage of parasitic protozoa such as Cryptosporidium parvum and Giardia lamblia. Cysts are shed in animal and human feces, enter water systems through agricultural runoff, and are highly resistant to chlorination — Cryptosporidium is essentially immune to chlorine at normal treatment doses. The EPA's Surface Water Treatment Rule requires utilities to achieve 99% cyst removal. Effective removal requires either 0.5-micron absolute filtration (NSF 53/58 certified carbon block or RO) or UV disinfection with sufficient intensity. Cyst contamination risk increases after heavy rainfall events that overwhelm surface water treatment capacity.

Total Dissolved Solids (TDS) is a measure of all inorganic and organic substances dissolved in water — expressed in milligrams per liter (mg/L) or parts per million (ppm). Measured with a TDS meter (electrical conductivity). TDS includes minerals (calcium, magnesium, sodium, potassium), heavy metals, chlorides, sulfates, and organic compounds. High TDS doesn't automatically mean unsafe water — most Austin TDS (300–450 ppm) is composed of beneficial minerals. TDS meters are often used to verify RO system performance: a well-functioning RO should reduce TDS by 85–98%. WHO guideline: below 600 ppm is generally acceptable; above 1,000 ppm affects taste noticeably.

A water softener system with two resin tanks (plus a shared brine tank) that alternates between tanks during regeneration. While one tank regenerates, the other continues softening — providing uninterrupted soft water 24/7. Single-tank softeners typically produce hard water during their 1–2 hour regeneration cycle (usually 2 AM). Dual-tank systems are recommended for households with high water usage (5+ people), commercial applications, or homes where water quality cannot be interrupted.

The outflow from a water treatment system — the treated water exiting a filter, softener, or RO unit. In the context of RO systems, effluent refers to the product water (purified water) that passes through the membrane. Contrast with brine waste or concentrate — the rejected water stream that carries removed contaminants to drain. Effluent quality is measured by comparing TDS, hardness, or specific contaminant levels before and after treatment.

The accumulation of unwanted material on a filter membrane, media, or surface — reducing flow rate and filtration effectiveness. Types of fouling include: particulate fouling (sediment clogging), biological fouling (biofilm growth), scaling fouling (mineral deposits, especially calcium carbonate), and organic fouling (natural organic matter adhesion). RO membranes are particularly vulnerable to fouling. Proper pre-treatment (sediment filters upstream of membranes) significantly reduces fouling and extends membrane life from 2–3 years to 5+ years.

A water treatment process where fine particles (colloids, clay, silt) are caused to clump together into larger aggregates called "floc" that can then be removed by sedimentation or filtration. Achieved by adding chemical coagulants (aluminum sulfate, ferric chloride, or polymers) that neutralize the electrical charge keeping particles suspended. Used extensively in municipal water treatment plants. Not typically used in residential point-of-use systems — residential filtration relies on physical filtration rather than flocculation. Austin Water's Ullrich and Davis water treatment plants use flocculation as the second stage of treatment.

The total grains of hardness a water softener can remove before its resin is exhausted and must regenerate. Common residential sizes: 24,000; 32,000; 48,000; 64,000 grains. To size a softener: daily grains to remove = people × 80 gallons/day × GPG hardness. Divide your softener's grain capacity by this number to find days between regenerations (target: 7–14 days). A correctly sized softener regenerates efficiently without wasting salt; an oversized one regenerates less but salt is wasted during each cycle; an undersized one regenerates too frequently and may not fully soften.

A rating used to describe RO membrane production capacity — how many gallons of purified water the system can produce in 24 hours. Common residential ratings: 50, 75, 100, 150 GPD. Production rate is affected by water temperature (slows in cold) and incoming water pressure (faster at higher pressure). A 75 GPD system produces about 3 gallons per hour — enough for most families if combined with a storage tank. Do not confuse with flow rate (gallons per minute), which measures how fast water flows at a tap.

A colorless gas with a distinctive rotten egg odor, dissolved in water. Produced by sulfur-reducing bacteria in groundwater, from decomposing organic matter, or from geological sulfur deposits. Even at very low concentrations (0.05 ppm), it's detectable by smell. At higher levels it corrodes copper pipes and silver fixtures (black tarnishing). Removed by aeration, oxidation (with chlorine, ozone, or hydrogen peroxide injection), or catalytic carbon filtration. Well water in the Texas Hill Country — particularly from the Cretaceous limestone and Ellenburger dolomite formations — is a common source.

A group of disinfection byproducts formed when chlorine or chloramine reacts with natural organic matter (humic acids, fulvic acids) in source water. The five regulated species — monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid — are collectively regulated under HAA5. The EPA MCL is 60 μg/L. Long-term exposure above MCL is associated with increased liver, kidney, and nervous system effects. Reduced by maintaining lower organic matter in source water and by activated carbon or RO treatment at the point of use.

The core mechanism of water softeners — a reversible chemical process in which ions in solution are exchanged for similarly charged ions attached to a solid resin matrix. In a water softener, a cation exchange resin (tiny polystyrene beads) carries sodium ions (Na⁺). As hard water passes through, calcium (Ca²⁺) and magnesium (Mg²⁺) ions — both divalent cations — are attracted to the resin with higher affinity than sodium, displacing sodium ions into the water. The resin holds the hardness ions; sodium enters the treated water. During regeneration, concentrated brine reverses this exchange, loading sodium back onto the resin and flushing calcium/magnesium to drain.

A whole-house filtration system designed to remove dissolved iron (ferrous/Fe²⁺) and particulate iron (ferric/Fe³⁺) from water. Iron in water causes rust staining on fixtures and laundry, imparts a metallic taste, and clogs pipes over time. Iron filters typically use one of three technologies: oxidation + filtration (air injection or potassium permanganate oxidizes dissolved iron so it can be filtered), birm media (catalytic oxidation), or KDF media. Well water in Bastrop, Cedar Creek, and east of Austin commonly contains iron at 0.5–5 ppm. EPA secondary standard (aesthetic): 0.3 ppm.

Kinetic Degradation Fluxion (KDF) is a high-purity copper-zinc granular alloy that removes chlorine, heavy metals, and controls scale through a redox (oxidation-reduction) reaction. When water contacts KDF, electrons transfer between copper and zinc ions and contaminant molecules — converting chlorine to chloride (harmless), removing lead, mercury, and cadmium through electrochemical plating, and inhibiting bacterial growth. KDF is typically combined with activated carbon in shower filters and whole-house systems. KDF 55 targets dissolved chlorine and hydrogen sulfide; KDF 85 targets iron and hydrogen sulfide.

The core filtration element of a reverse osmosis system — a semi-permeable thin-film composite (TFC) membrane wound in a spiral configuration around a central collection tube. RO membranes have pore sizes of approximately 0.0001 microns (0.1 nanometers) — small enough to block virtually all dissolved contaminants, heavy metals, bacteria, viruses, nitrates, fluoride, arsenic, and most pharmaceuticals, while allowing water molecules through. Water molecules are small enough to pass through gaps in the polymer chain; nearly everything else is too large. Typical residential RO membranes last 2–5 years and should be replaced when TDS rejection drops below 85%.

A unit of length equal to one millionth of a meter (0.001 mm). Used to express filter pore size — the smaller the micron rating, the finer the filtration. Reference scale: human hair = 70 μm; pollen = 10 μm; bacteria = 0.2–2 μm; viruses = 0.02–0.4 μm; RO membrane pores = 0.0001 μm. Nominal vs. absolute rating: a nominal 5-micron filter removes ~85% of particles at 5 μm; an absolute 5-micron filter removes 99.9%+ at that size. Absolute ratings are used for applications requiring regulatory compliance (cyst removal, lead removal).

A naturally occurring metallic element that dissolves into groundwater from sedimentary rock. In water, manganese causes black or brownish-black staining on fixtures, laundry, and dishwashers — distinct from the reddish-orange staining of iron. EPA secondary MCL (aesthetic): 0.05 mg/L; primary health-based guideline (EPA draft): 0.1 mg/L. Elevated manganese is associated with neurological effects with long-term exposure. Removed by oxidation (chlorine, ozone, potassium permanganate) followed by filtration, or by greensand/birm media. Often co-occurs with iron in well water.

NSF International (formerly the National Sanitation Foundation) is an independent organization that tests and certifies water treatment products against documented performance standards. Key NSF standards for residential water treatment: NSF/ANSI 42 — aesthetic effects (chlorine taste/odor, zinc reduction); NSF/ANSI 44 — cation exchange water softeners; NSF/ANSI 53 — health effects (lead, cysts, VOCs); NSF/ANSI 58 — reverse osmosis systems; NSF/ANSI 61 — drinking water system components (no leaching); NSF/ANSI 401 — emerging contaminants (pharmaceuticals, PFAS). Always verify the specific standard a product is certified to — "NSF certified" without a standard number is meaningless marketing.

Osmosis is the natural movement of water molecules through a semi-permeable membrane from a region of low solute concentration to high concentration — driven by osmotic pressure. Reverse osmosis (RO) applies pressure greater than the osmotic pressure to force water through the membrane in the opposite direction — from high concentration to low — leaving contaminants behind. Pressure required: typically 40–80 psi for residential use (Austin Water normally delivers 60–80 psi). RO rejects 85–98% of dissolved solids, heavy metals, nitrates, fluoride, arsenic, pharmaceuticals, PFAS, and virtually all bacteria and viruses. Rejected contaminants exit as concentrate (brine) to drain.

A chemical reaction in which a substance loses electrons — in water treatment, used to convert dissolved (soluble) contaminants into an insoluble precipitate that can be filtered. Iron oxidation: Fe²⁺ (dissolved, invisible) + O₂ → Fe³⁺ (precipitates as rust particles, filterable). Oxidizing agents used in water treatment include: chlorine, hydrogen peroxide, ozone, potassium permanganate, and air (aeration). Ozone is the most powerful water treatment oxidant and also disinfects; chlorine is the most widely used. Over-oxidation can create disinfection byproducts.

A logarithmic scale (0–14) measuring the concentration of hydrogen ions (H⁺) in water — a measure of acidity or alkalinity. pH 7 = neutral; below 7 = acidic; above 7 = alkaline/basic. Each pH unit represents a 10× change in H⁺ concentration. EPA secondary standard for drinking water: 6.5–8.5. Low pH (acidic) water is corrosive and can leach lead and copper from pipes. High pH (alkaline) water can taste bitter and may indicate high carbonate mineral content. Austin municipal water is typically maintained at pH 7.4–7.8 to minimize pipe corrosion. RO permeate is typically acidic (pH 5.5–6.5) due to dissolved CO₂ — some RO systems add a remineralization stage to raise pH.

Two categories defining where in the plumbing system water treatment occurs. Point of Entry (POE) systems — also called "whole-house" — treat all water entering the home at the main supply line before it reaches any tap, shower, appliance, or toilet. Examples: whole-house carbon filters, water softeners, UV disinfection. Point of Use (POU) systems treat water at a specific outlet — typically the kitchen tap. Examples: under-sink RO systems, faucet-mount filters, pitcher filters. For Austin, the optimal approach is often a POE softener + carbon filter (protects appliances and skin throughout the house) combined with a POU RO system (provides highest-purity drinking water at the kitchen).

The recharging cycle of a water softener that restores the ion-exchange resin to full sodium-loaded capacity. Process: (1) Backwash — water reverses to loosen and flush the resin bed; (2) Brine draw — concentrated salt solution slowly flows through the resin, displacing calcium/magnesium ions and replacing them with sodium; (3) Rinse — excess brine and displaced hardness ions are flushed to drain; (4) Service — the softener returns to normal operation. A full regeneration uses 30–65 gallons of water and 5–15 lbs of salt. Demand-initiated regeneration (DIR) systems regenerate based on actual water usage rather than a timer — using 20–30% less salt than timer-based systems.

The ion-exchange medium in a water softener — millions of tiny polystyrene beads (0.3–1.2 mm diameter) cross-linked with divinylbenzene (DVB) to provide structural stability. Each bead is a three-dimensional polymer matrix with fixed negatively charged sulfonate groups (SO₃⁻) that attract positively charged cations. Standard softener resin: 8% DVB cross-linking, strong acid cation (SAC) type. Fine mesh resin (10% DVB): more durable, better iron resistance. High-capacity resin lasts 15–20 years if protected from iron fouling and chlorine degradation — both of which are concerns in Austin. The SS1's resin is rated at 32,000 grain capacity.

The process of adding beneficial minerals back to water after aggressive filtration (particularly RO) has removed both contaminants and naturally occurring minerals. RO permeate is essentially mineral-free (TDS 5–30 ppm) and slightly acidic — which, while safe, tastes flat and may be corrosive to copper pipes. Remineralization typically adds calcium and magnesium using calcite (calcium carbonate) media cartridges or coconut shell carbon + mineral stages. A 5-stage RO with remineralization produces water closer to natural spring water — slightly alkaline, with a balanced mineral taste. Some argue demineralized water is also nutritionally suboptimal with long-term exclusive consumption.

A mechanical filter that removes suspended particles — sand, silt, clay, rust flakes, and other particulates — from water. Rated by micron size: 50-micron filters remove coarse sediment; 5-micron filters remove fine particles; 1-micron filters approach bacteria-sized particles. Always installed as the first stage in any multi-stage system — before carbon filters, softeners, and especially before RO membranes (which foul quickly with particulate). Sediment filters are typically spun polypropylene or pleated polyester cartridges, replaced every 3–6 months. Well water users often require 50-micron pre-filtration before any other treatment.

Water that has had its calcium and magnesium ions removed via ion exchange and replaced with sodium ions. Softened water: lathers readily with soap; does not form scale; does not leave mineral deposits on surfaces; extends appliance and plumbing lifespan. Concerns: softened water contains elevated sodium — at 15 GPG, softening adds approximately 115 mg of sodium per liter (the WHO guideline is 200 mg/L; a typical softened water still falls well below this). Persons on strict sodium-restricted diets should use a potassium chloride (KCl) alternative to salt, or install a separate drinking water RO tap that bypasses the softener. Softened water should not be used to water sodium-sensitive plants.

A water treatment technology that does not remove hardness minerals but transforms their crystalline structure from calcite (adherent scale) to aragonite (non-adherent microcrystals that stay suspended and pass through plumbing). Uses polymer media beads with nucleation sites. TAC/salt-free conditioners produce no wastewater, use no salt, require no electricity, and do not add sodium to water. The tradeoff: water is not "softened" in the traditional sense — hardness ions remain, meaning soap still lathers less than with true softened water, and the scale-prevention benefit on heating elements is less complete. Often marketed as "water softeners" — technically they are scale inhibitors.

A handheld device that measures Total Dissolved Solids via electrical conductivity (EC) — dissolved ions carry electrical current, and more ions = higher conductivity = higher TDS reading. Results in parts per million (ppm) or mg/L. Simple, inexpensive ($10–20), and instant. Limitations: TDS meters cannot distinguish between beneficial minerals and harmful contaminants — high-TDS "spring water" and high-TDS arsenic-contaminated well water might give the same reading. Useful for verifying RO system performance (before vs. after TDS should drop 85–98%) and for monitoring membrane condition over time. Not a substitute for a full water test.

The cloudiness or haziness of water caused by suspended particles (sediment, clay, algae, microorganisms). Measured in Nephelometric Turbidity Units (NTU) using a turbidimeter that shines light through a water sample and measures scattering. EPA MCL for treated surface water: 0.3 NTU (with a maximum of 1 NTU at any time). High turbidity is aesthetically unpleasant, indicates potential microbial contamination (pathogens can hide inside particles, protecting them from disinfection), and is used as an indirect indicator of treatment effectiveness. Austin's treated water typically runs 0.05–0.1 NTU. Turbidity spikes significantly after heavy rain events due to Colorado River runoff.

The most regulated class of disinfection byproducts — formed when chlorine or chloramine reacts with naturally occurring organic matter. The four regulated species are chloroform (CHCl₃), bromodichloromethane, dibromochloromethane, and bromoform — collectively regulated as TTHMs. EPA MCL: 80 μg/L. Long-term exposure above MCL is associated with increased bladder cancer risk and adverse birth outcomes. Levels are highest in summer (warmer temperatures, more organic matter in source water). Plain chlorine produces higher TTHMs than chloramine; this is partly why Austin switched to chloramine in 2007. Point-of-use activated carbon or RO removes essentially all TTHMs.

A point-of-use filtration system installed beneath the kitchen sink — either a multi-stage carbon filter system or a full reverse osmosis system. Connected to the cold water supply line; dispenses treated water through a dedicated filtered-water tap (separate from the main faucet) or through the main faucet via a diverter. Advantages over pitcher filters: higher flow rate, larger capacity, no manual filling required. Advantages over whole-house systems: treats only drinking/cooking water at higher purity (e.g., RO removes contaminants that whole-house carbon filters cannot). Most common configuration for Austin homeowners: whole-house carbon + softener (POE) + under-sink RO (POU).

A chemical-free disinfection method that exposes water to ultraviolet light (wavelength 254 nm) — disrupting the DNA and RNA of bacteria, viruses, and cysts, preventing them from reproducing (effectively killing them). Effective against all known waterborne pathogens including Cryptosporidium and Giardia (which are chlorine-resistant). UV does not remove chemical contaminants, heavy metals, or dissolved solids — it is a disinfection-only technology typically used as the last stage in a treatment system, after filtration (turbid water blocks UV penetration). No chemicals are added; water chemistry is unchanged. Essential for well water that lacks municipal chemical disinfection.

A broad category of organic chemical compounds with high vapor pressure — they evaporate readily at room temperature (hence the "volatile" designation). In drinking water, VOCs include industrial solvents (benzene, toluene, TCE, PCE), fuel compounds (MTBE), and some agricultural chemicals. Many are known or suspected carcinogens. Sources: gasoline spills, dry-cleaning chemicals, industrial discharge, leaking underground storage tanks. VOC contamination is more common in groundwater (wells) than treated municipal water. Removed effectively by activated carbon filtration (GAC or carbon block) and by RO. The EPA regulates 32 VOCs in drinking water under the SDWA.

The ratio of concentrate (drain) water to purified (product) water in a reverse osmosis system. Traditional RO systems produce approximately 1 gallon of purified water for every 3–4 gallons sent to drain (25–33% efficiency; 3:1 to 4:1 waste ratio). More efficient "permeate pumps" or "zero-waste" designs using concentrate recycling can achieve 1:1 ratios or better. Waste ratio is affected by: water pressure (higher = more efficient), temperature (warmer = more efficient), membrane condition, and TDS of incoming water. For Austin water at 350 ppm TDS and 65 psi, a well-maintained modern RO typically achieves approximately 2:1 waste ratio.

A Point of Entry (POE) filtration system installed on the main water supply line entering the home — treating all water used for drinking, cooking, bathing, laundry, and appliances. A whole-house filter addresses contaminants that affect the entire home, particularly chloramine (which off-gasses in showers and can be inhaled), volatile chemicals, and sediment. The SpringWell CF1 is an example: a 4.5" × 20" catalytic carbon media tank with a digital control head for automated backwashing. Contrast with under-sink or pitcher filters that treat water only at one tap. Most Austin homeowners benefit most from a catalytic carbon whole-house filter combined with a water softener.

One of the world's largest water technology companies (NYSE: XYL) — provides infrastructure, analytics, testing, and treatment solutions primarily for commercial, municipal, and industrial applications. Products include pumps, meters, valves, treatment systems, and monitoring equipment. Xylem owns brands including Sensus (smart meters), YSI (water quality instruments), and Flygt (submersible pumps). In residential water treatment, Xylem is better known in the professional/commercial space rather than consumer retail. Mentioned here because homeowners may encounter the name when researching water quality monitoring equipment or commercial-grade treatment systems.

A group of naturally occurring and synthetic aluminosilicate minerals with highly porous, crystalline structures — used in water treatment for ion exchange, adsorption, and catalysis. Natural zeolites (clinoptilolite) are used in some water softeners as an alternative to synthetic polystyrene resin. Synthetic zeolites are used in municipal water treatment as catalytic media. In residential applications, zeolite media is used in some softeners and whole-house systems as a natural, mined alternative to plastic-based ion exchange resin. Capacity and performance are generally lower than high-quality synthetic resin, but zeolite is biodegradable and considered more environmentally friendly.

Refers to water treated to near-zero Total Dissolved Solids — typically below 10 ppm. Achieved through deionization (DI), distillation, or RO with a polishing stage. ZeroWater is also a consumer pitcher filter brand that uses a 5-stage ion exchange system to achieve 000 ppm TDS readings. Ultra-low TDS water has a very flat, slightly metallic taste (minerals contribute to water flavor), can be corrosive to copper pipes, and provides no mineral nutrition. For most health and culinary applications, water with 50–150 ppm TDS (slightly mineralized RO or spring water) is considered optimal. TDS 000 ppm is most useful for laboratory applications, aquariums, and steam irons.