The simplest way to discover how contaminated your water may be is to use a special meter that measures ‘Total Dissolved Solids’ (TDS) such as salts, minerals and other stuff that can be harmful, including metals and chemicals. The lower the TDS, the ‘purer’ your water may be.
TDS is measured on a quantity scale, either in mg/liter or, more commonly, in parts per million (PPM). Simply put, if the TDS level is 1,000 mg/l or 1,000 PPM, it means that out of one-million parts of H20, 1,000 of those parts comprise something else.
The lower the level, the better. TDS levels exceeding 1,000 mg/l is a general indication that the water is undrinkable. The U.S. Environmental Protection Agency (EPA) suggests a limit of 500 mg/l, however. Water registering a TDS level of 0 – 50 can be considered pretty good.
High TDS levels may reveal the possible presence of toxic substances such as lead, arsenic, nitrate and more nasty stuff. It can also lead to water tasting salty, bitter or metallic. And it indicates the water may be ‘hard’, containing high amounts of calcium and magnesium, which can discolor plates and glasses as well as cause damage to dishwashers, washing machines and coffee makers, for example.
TDS meters are pretty accurate at showing the total dissolved solids in tap water, but they will not specify exactly what those solids are. To find out what is in your tap water you’d have to use a much more expensive system or send samples to a testing laboratory.
“Refer to your TDS device manual for detailed instructions and remember that TDS meters can vary. Shake:
Always make sure to shake excess water off the meter before dipping it into a water sample, even if it’s the same water.
After dipping the meter in the water, always lightly tap it against the side and stir the meter to remove any lingering air bubbles or electrical charges.
When taking the reading, always make sure to hold the meter straight up without it touching the sides or bottom of the glass/beaker/cup. The probes should be suspended as close to the center of the water sample as possible.
The longer the meter is in the water, the more accurate the reading will be.
25 degrees Celsius is the ideal temperature for conductivity readings, even if the meter has ATC.
If switching between very low and very high ppm water, always rinse the probes with distilled water to avoid any build-up.”
Conductivity of ions in water depends upon temperature. There are a number of factors that cause this effect, but a major one is simply that the ions naturally move around faster as they get warmer. When the same numbers of ions are moving faster, the apparent conductivity is increased. The relationship between conductivity and temperature is complicated and dependent on the solution being tested.
Pure water responds fairly linearly with temperature, with its conductivity rising by 4.55% for every degree centigrade (2.5% per degree Fahrenheit). Sodium chloride solutions have a smaller change, about 2.12% per degree centigrade. Tap and other natural waters have many different ions in them, and such systems sometimes respond nonlinearly with temperature changes, but not typically to as great of an extent as does pure water.
For this reason, nearly all conductivity meters simultaneously measure the conductivity and the temperature.”
The EPA sets a maximum level 500 PPM, although we would say anything above 170 PPM can be considered as ‘hard’ and will not taste as pure as nature intended.