TDS Calculator

What is TDS and why should I care?

Total Dissolved Solids (TDS) refers to the combined amount of inorganic and organic substances dissolved in water, such as minerals, salts, metals, and small amounts of organics. When you test your tap or RO water, TDS gives you an indicator of how loaded the water is with these dissolved substances. Understanding your TDS helps you ensure your water filtration system is doing its job and that your water quality is in a good range for taste, appliances, and health.

How do I test for TDS at home?

Testing for TDS is simple. Use a pocket TDS meter to measure your tap or feed water. Rinse it properly, then measure your treated or filtered (for example, RO) water. Enter those two values into our calculator to see how effective your membrane is. A large difference between the feed and treated values means your system is doing a good job reducing dissolved solids. If your meter reading is high for the treated water, it may signal that maintenance is needed.

What is a good TDS level in household water?

There is no single perfect number for all households, but generally, lower is better for drinking and filtered water. If your RO-treated water shows a TDS reading in the low tens (ppm) while your tap water is much higher, that is a strong result. If your membrane effectiveness is between 75% and 100%, your system is operating within normal specifications. If it is below 75%, you may need to change the filters or membrane.

What should I do if my membrane rejection rate is low?

If your calculated rejection rate is lower than expected, for example, below 75%, try the following steps:

• Check that your pre and post filters are fresh and properly installed.
• Make sure the flow restrictor is correct and system pressure is within range.
• Replace the RO membrane if it is old or has been exposed to high TDS feed water for a long time.
• Review the feed water TDS reading. If it is extremely high, it may reduce the membrane's life and performance over time.

Proper maintenance can restore system performance and protect your drinking water quality.

Why does my tap water TDS change, and does it matter?

Your tap water TDS can vary over time due to changes in the water source, seasonal variations, treatment processes, or plumbing conditions. A gradual increase in tap TDS might mean more dissolved minerals or salts are entering your supply. While TDS alone does not specify which substances are present, a rising level may be a signal to check your water filtration system or consider additional treatment, such as pre-filtration or water softening.

How does TDS relate to other water quality factors?

TDS is one indicator of water quality, but not the only one. Low TDS does not always mean the water is safe, and high TDS does not necessarily mean it is unsafe. Harmful contaminants like bacteria or heavy metals might not show up in a TDS reading. Likewise, water with high mineral content (and higher TDS) may not pose a health risk but could affect taste, scale buildup, or appliance lifespan. It is a good idea to pair a TDS test with a broader water quality evaluation or to use certified filters and RO systems as part of your home's water treatment plan.