{"id":132,"date":"2026-05-11T13:50:43","date_gmt":"2026-05-11T08:50:43","guid":{"rendered":"https:\/\/watertankcalculator.com\/guides\/?p=132"},"modified":"2026-05-11T13:50:44","modified_gmt":"2026-05-11T08:50:44","slug":"what-is-tds-in-water-and-why-does-it-matter-for-storage","status":"publish","type":"post","link":"https:\/\/watertankcalculator.com\/guides\/what-is-tds-in-water-and-why-does-it-matter-for-storage\/","title":{"rendered":"What Is TDS in Water and Why Does It Matter for Storage?"},"content":{"rendered":"\n

Total Dissolved Solids (TDS)<\/strong> is the combined concentration of all inorganic and organic substances dissolved in water \u2014 measured in milligrams per litre (mg\/L) or parts per million (ppm), where 1 mg\/L = 1 ppm. It includes calcium, magnesium, sodium, potassium, carbonates, chlorides, sulfates, and trace amounts of metals and organics. TDS does not measure bacteria or suspended particles \u2014 it specifically captures what is chemically dissolved and invisible to the naked eye.<\/p>\n\n\n\n

Use the TDS water calculator<\/a> to assess your stored water quality against WHO and national drinking standards.<\/p>\n\n\n\n

What TDS Levels Mean in Practice<\/h2>\n\n\n\n
TDS Level (ppm)<\/strong><\/td>Classification<\/strong><\/td>Taste Profile<\/strong><\/td>Suitable For<\/strong><\/td><\/tr>
< 50<\/td>Very low<\/td>Flat, bland<\/td>Not recommended for prolonged drinking<\/td><\/tr>
50\u2013150<\/td>Low<\/td>Clean, slightly bland<\/td>Drinking, cooking, RO permeate<\/td><\/tr>
150\u2013300<\/td>Acceptable<\/td>Neutral to pleasant<\/td>Ideal for drinking<\/td><\/tr>
300\u2013600<\/td>Moderate<\/td>Slightly mineral<\/td>Acceptable for drinking<\/td><\/tr>
600\u2013900<\/td>High<\/td>Noticeably mineral<\/td>Marginal for drinking; taste complaints common<\/td><\/tr>
900\u20131,200<\/td>Very high<\/td>Salty or metallic<\/td>Not recommended for drinking<\/td><\/tr>
> 1,200<\/td>Unsafe<\/td>Strongly saline<\/td>Unsuitable for human consumption<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The WHO guideline for drinking water is 600 ppm<\/strong>, though palatability typically declines above 300 ppm. Most national standards cap acceptable TDS between 500 and 1,000 ppm. India’s BIS standard sets 500 ppm as desirable and 2,000 ppm as the maximum permissible limit. The US EPA sets a secondary standard of 500 ppm (non-enforceable, taste-based).<\/p>\n\n\n\n

Why TDS Changes During Tank Storage<\/h2>\n\n\n\n

Water sitting in a tank does not stay chemically static. Several mechanisms alter TDS over time. First, evaporation from open or poorly sealed tanks removes pure water vapour but leaves dissolved solids behind \u2014 concentrating TDS in the remaining water. In hot climates with high evaporation rates, a tank losing 5% of its volume to evaporation will see TDS rise by approximately 5%.<\/p>\n\n\n\n

Second, concrete and metal tanks leach minerals into stored water. Freshly cured concrete tanks add calcium hydroxide and other alkalis, which raises TDS and pH simultaneously. Corroding iron or galvanised steel tanks contribute iron and zinc ions. Plastic tanks are largely inert but can leach additives if they are low-grade or degraded by UV exposure.<\/p>\n\n\n\n

Third, biological activity in improperly treated or uncovered tanks produces metabolic by-products that contribute to organic TDS. Algae and biofilm formation can raise TDS measurably in warm, light-exposed storage.<\/p>\n\n\n\n

If you are treating stored water with chlorine, the residual chlorine reacts with organic matter to produce disinfection by-products \u2014 adding to TDS. Use the chlorine dosage calculator<\/a> to dose accurately and avoid over-chlorination.<\/p>\n\n\n\n

TDS and Storage Safety: What the Number Does Not Tell You<\/h2>\n\n\n\n

TDS is a proxy measure, not a safety guarantee. Low TDS water is not automatically safe \u2014 pathogens, pesticides, and industrial contaminants may be present at dangerous levels while TDS reads below 100 ppm. Conversely, high-TDS water from a mineral-rich aquifer may be microbiologically safe but taste unpleasant and cause scaling in appliances.<\/p>\n\n\n\n

TDS testing should always be paired with pH testing and, where there is any doubt about the source, microbiological testing. The water pH adjustment calculator<\/a> helps correct pH imbalances that often accompany abnormal TDS readings.<\/p>\n\n\n\n

For long-term tank storage, TDS alone cannot confirm water is safe to drink after several weeks. Combine TDS measurement with a residual chlorine check and a visual inspection for sediment, colour change, or odour.<\/p>\n\n\n\n

TDS Thresholds for Specific Uses<\/h2>\n\n\n\n
Application<\/strong><\/td>Maximum TDS (ppm)<\/strong><\/td>Notes<\/strong><\/td><\/tr>
Drinking water (WHO)<\/td>600<\/td>Taste acceptable up to ~300 ppm<\/td><\/tr>
Baby formula preparation<\/td>< 100<\/td>Low mineral content required<\/td><\/tr>
Aquarium (freshwater)<\/td>< 500<\/td>Species-dependent<\/td><\/tr>
Hydroponics \/ irrigation<\/td>< 1,500<\/td>Depends on crop type<\/td><\/tr>
Livestock (cattle)<\/td>< 3,000<\/td>Short-term tolerance higher<\/td><\/tr>
Reverse osmosis membrane<\/td>< 2,000 feed<\/td>Higher TDS accelerates membrane fouling<\/td><\/tr>
Boiler\/hot water system<\/td>< 200<\/td>Scaling risk above this level<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Common Mistakes<\/h2>\n\n\n\n

Mistake 1: Treating TDS as a pass\/fail safety test.<\/strong> A TDS reading of 250 ppm tells you the total dissolved load but nothing about what is dissolved. Arsenic contamination, nitrates, and E. coli are invisible to a TDS meter. Use TDS as a screening tool and first-line quality indicator, not as a definitive safety assessment.<\/p>\n\n\n\n

Mistake 2: Ignoring TDS rise in sealed tanks during extended storage.<\/strong> Even sealed tanks concentrate dissolved solids slowly over weeks due to minor evaporation through vents and leaching from tank materials. Water stored longer than 30 days should be re-tested. The safe water storage duration calculator<\/a> estimates how long treated water remains safe under your conditions.<\/p>\n\n\n\n

Mistake 3: Interpreting very low TDS (under 50 ppm) as superior quality.<\/strong> RO-purified or distilled water with near-zero TDS is demineralised. Prolonged consumption of very low-TDS water leaches minerals from body tissue over time and can be mildly corrosive to metal plumbing. The WHO recommends a minimum of 100 ppm for regular drinking water.<\/p>\n\n\n\n

Mistake 4: Testing TDS once and assuming it stays constant.<\/strong> TDS changes with season, supply source variation, tank condition, and treatment. Test at minimum quarterly for stored water, and after any change to the supply source or tank.<\/p>\n\n\n\n

Related Calculators You Might Need<\/h2>\n\n\n\n

TDS is one part of a broader water quality picture. If your TDS is elevated due to water hardness, the water hardness calculator<\/a> will tell you whether scaling is a risk for your appliances and pipes. If the storage itself is the source of contamination, the water tank disinfection calculator<\/a> guides you through a cleaning protocol. For water that requires UV treatment rather than chemical dosing, the UV disinfection tank calculator<\/a> sizes the system correctly for your flow rate. And if you are purchasing a filtration unit to reduce TDS, confirm it can handle your demand with the water filter flow rate calculator<\/a>.<\/p>\n\n\n\n

Frequently Asked Questions<\/h2>\n\n\n\n

What is a good TDS level for drinking water?<\/strong><\/p>\n\n\n\n

Between 150 and 300 ppm is considered ideal for drinking water \u2014 enough minerals for taste and health, below the threshold where most people notice off-flavours. Water in the 300 to 600 ppm range is acceptable but may taste noticeably mineral. Above 600 ppm, WHO considers the water outside its palatability guideline. Below 50 ppm is demineralised and not recommended for regular long-term consumption.<\/p>\n\n\n\n

Can high TDS make you sick?<\/strong><\/p>\n\n\n\n

High TDS alone is not acutely toxic for most people. The health concern depends entirely on what is causing the high reading. Elevated TDS from calcium and magnesium is generally harmless. TDS elevated by nitrates, arsenic, heavy metals, or industrial contaminants is a direct health hazard at much lower concentrations. A TDS meter cannot distinguish between these \u2014 laboratory analysis is needed to identify specific ions.<\/p>\n\n\n\n

How do I reduce TDS in my storage tank?<\/strong><\/p>\n\n\n\n

The only effective method is to treat or replace the water. Reverse osmosis reduces TDS by 90 to 98%. Distillation removes nearly all dissolved solids. Ion exchange softeners reduce hardness-related TDS. Boiling does not reduce TDS \u2014 it concentrates it by driving off pure water as steam. If TDS is rising due to tank leaching, the tank surface needs cleaning or lining.<\/p>\n\n\n\n

Does chlorination affect TDS?<\/strong><\/p>\n\n\n\n

Yes. Adding chlorine or bleach to water introduces sodium, chloride ions, and disinfection by-products \u2014 all of which raise TDS slightly. A standard shock dose for tank disinfection typically adds 5 to 15 ppm to TDS, which is negligible for most applications. Accurate dosing matters: the bleach to water ratio calculator<\/a> prevents over-dosing that would unnecessarily spike TDS and create off-flavours.<\/p>\n\n\n\n

Why does my TDS reading spike after heavy rainfall fills the tank?<\/strong><\/p>\n\n\n\n

Roof runoff carries atmospheric dust, bird droppings, leaf decomposition products, and surface contaminants \u2014 all of which dissolve in the collected water and raise TDS. First-flush events (the first few minutes of rainfall) carry the highest contamination load. A first-flush diverter removes the most contaminated initial runoff before it reaches the tank, protecting baseline TDS. After major rain events, re-test TDS before using the stored water for drinking.<\/p>\n","protected":false},"excerpt":{"rendered":"

Total Dissolved Solids (TDS) is the combined concentration of all inorganic and organic substances dissolved in water \u2014 measured in milligrams per litre (mg\/L) or parts per million (ppm), where 1 mg\/L = 1 ppm. It includes calcium, magnesium, sodium, potassium, carbonates, chlorides, sulfates, and trace amounts of metals and organics. TDS does not measure […]<\/p>\n","protected":false},"author":1,"featured_media":76,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5,1],"tags":[],"class_list":["post-132","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-concepts-explainers","category-blog"],"_links":{"self":[{"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/posts\/132","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/comments?post=132"}],"version-history":[{"count":1,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/posts\/132\/revisions"}],"predecessor-version":[{"id":136,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/posts\/132\/revisions\/136"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/media\/76"}],"wp:attachment":[{"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/media?parent=132"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/categories?post=132"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/watertankcalculator.com\/guides\/wp-json\/wp\/v2\/tags?post=132"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}