Total Dissolved Solids: Explained

Warm weather will be here before we know it and that means it’s time to give your swimming pool the attention it’s been craving. One of the first things you might do is bring a sample of your pool water to your local swimming pool supply store to have it tested. The results might show that your TDS levels are high and draining your pool can help with the problem. So what exactly does it mean to have high TDS levels?

Aqua Magazine’s February 2019 edition contains an interesting article explaining Total Dissolved Solids (TDS)1. Although quite informative, the feature was quite lengthy and complex so I thought I’d take a moment to simplify it a bit. If you’d like to read Aqua Magazine’s full article you can find it here


TDS is an acronym for Total Dissolved Solids. Two types of solids can be found in your pool, suspended and dissolved. Suspended solids are cleared from the pool with the help of your swimming pool’s filtration system. The dissolved solids in ionic suspension historically were only removed by draining the pool. New technology now allows us to clear these dissolved solids by recycling the pool water through a reverse osmosis system thus saving thousands of gallons of water from being wasted.

When your pool supply store tells you that your TDS levels are high and it’s time to drain your pool, it means that your pool has accumulated minerals, metals, salts, and other contaminants.  TDS concentration increases over time as dissolved materials are added to the water from source or fill water, pool treatment chemicals, swimmer waste and environmental contaminants. Evaporation also increases TDS, as pure water evaporates leaving behind more concentrated dissolved solids.

In residential pools and spas, TDS testing should be performed monthly. In commercial pools, spas and water features, testing should be performed several times a month as necessary.


As a rule of thumb, maximum allowable TDS for pools and spas is 1,500 ppm greater than TDS levels at initial pool startup. Startup TDS includes balanced water TDS, from the fill source, as well as salt (sodium chloride) added at startup.

This maximum allowable level can be used to prevent issues associated with aging pool / spa water, such as:

  1. Reduced efficiency of disinfection / sanitizing chemicals due to elevated organic contaminants
  2. Corrosion of fixtures as TDS increases due to the greater conductivity of the water
  3. Surface staining and/or etching that can result from elevated TDS

Exceeding the maximum recommended TDS level may indicate the need to partially or completely drain water. (Provided drought conditions or other prohibitions against draining are not in effect.) Foothills Poolwater Revival’s Mobile Reverse Osmosis system can lower TDS levels to acceptable ranges without wasting Arizona’s precious water and often times will bring the TDS levels to below what is provided by city water.


Bring two water samples to your pool supply store to be tested for TDS. One sample will be from your home’s hose bib reflecting the original source water used to fill your pool. The second sample will be from your swimming pool. If the TDS of this original pool fill source water is measured and recorded to be 800 ppm and the TDS of the pool water now reads 2,500 ppm. The difference is greater than 1,500 ppm (2,500 ppm – 800 ppm = 1,700 ppm). Therefore, the pool should be drained immediately or processed through our reverse osmosis system.


Although there is not a minimum level in ANSI/APSP standards, source water TDS should always be checked before start-up of new pools, spas and water features. Low TDS may be indicative of low calcium hardness and/or low total alkalinity levels that may produce corrosive conditions that could affect tile grout, surfaces and equipment. High or elevated TDS levels (which include elevated sodium chloride levels) can:

  • Indicate high organic contamination, which can influence the consumption of the sanitizer and its ability to properly disinfect and oxidize the pool or spa water. That in turn can lead to swimmer or bather safety concerns.
  • Increase the conductivity of the water, which may lead to possible corrosion of fixtures, lights and equipment, especially if any stray voltage is present in the water.
  • Damage some Electronic Chlorine Generators (ECG), which should be monitored to prevent problems. Consult the ECG manufacturer to determine at what point high TDS can cause problems.
  • Lead to corrosion.


With increased TDS must come a heightened awareness of the potential problems associated with these elevated levels. Concerns with issues ranging from hazy “tired” water, improper water balances, surface staining, decreased sanitizer efficiency, and deterioration of equipment must all be considered with performing a regimen of care to any pool, spa, or water feature. One remedy to these problems is to perform a partial or complete drain of the pool and replace with fresh water that has a lower TDS content. Tucson Pool Water Recycling offers an alternative to a partial or complete drain and greatly benefits water conservation efforts in Arizona.

1 APSP Recreational Water Quality Committee. “Total Dissolved Solids: Explained.” Aqua February 2019: 34-37.