TCL - Total Contamination Level

Lishtot’s sensor’s output is the Total Contamination Level of the tested water.

This index is the most important index for user safety and it considers the full potential of the contaminants in the water to harm the drinker's health.


Drinking water without dangerous contaminants is very important to health. But the water could get pollution from multiple sources. Some of the contaminants come from natural sources but most of them are coming from man-made sources. Water pollution could be caused by sewage leaking into the drinking water system or it could be caused by industrial sources like factories and chemicals manufacturers.

There is a big lacuna in the existing water quality regulation. In the existing regulation water with high levels of multiple contaminants could be classified as “safe to drink” even though it contains very high levels of contaminants.

In order to understand how unsafe water could be defined as “safe” by the World Health Organization and the states authorities, it is important to understand the regulation. In the existing regulation, there is a Maximum Contamination Limit for about 160 contaminants. The water suppliers should meet this regulation and should supply water with fewer contaminants than the regulated threshold.

But what if the water contains more than one contaminant just below the threshold? What if the water contains not only Barium (Which could lead to increases in blood pressure) but also Lead, Thallium, Acrylamide, Carbofuran, p-Dichlorobenzene, and Simazine? All the above contaminants cause blood problems – is it safe to drink water with all of the above contaminants even if they are all just below the threshold?

So how the EPA or other authorities could allow the consumer to get water with so many contaminants?

The answer is that the regulator has no overall view of the water composition. There is a regulation that considers the presence of multiple different contaminants in the water, even if all of them could potentially harm the same human tissue.

In the reality, polluted water is usually containing a mix of contaminants the regulators didn’t adjust the regulation to the reality yet.

Total Contamination Level

Lishtot’s sensor is sensitive to multiple contaminants and the output of the sensor and the algorithm is a “Water Score” which is based on the total presence of contaminants in the water.

The water score, presented by the Lishtot app, reflects the presence of all the contaminants in the tested water. It could be that the water contains a high level of one contaminant or it could reflect the presence of lower level of multiple contaminants. In both cases, it is important to alert the user and give him the information regarding the water safety.


The EPA defined MCL and MCLG for water contamination as:


Maximum Contaminant Level Goal (MCLG) - The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals.


Maximum Contaminant Level (MCL) - The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards.

In many contaminants, the MCLG is 0 but the authorities still set the MCL to a higher level just because the water suppliers can’t supply better water.

In the table below you can find the list of the EPA regulated contaminants:

Contaminant MCLG (mg/L) MCL or TT (mg/L) Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
zero TT Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste
Giardia lamblia
zero TT Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste
Heterotrophic plate count (HPC)
n/a TT HPC has no health effects; it is an analytic method used to measure the variety of bacteria that are common in water. The lower the concentration of bacteria in drinking water, the better maintained the water system is. HPC measures a range of bacteria that are naturally present in the environment
zero TT Legionnaire's Disease, a type of pneumonia Found naturally in water; multiplies in heating systems
Total Coliforms (including fecal coliform and E. Coli)
zero 5.0% Not a health threat in itself; it is used to indicate whether other potentially harmful bacteria may be present Coliforms are naturally present in the environment; as well as feces; fecal coliforms and E. coli only come from human and animal fecal waste.
n/a TT Turbidity is a measure of the cloudiness of water. It is used to indicate water quality and filtration effectiveness (such as whether disease-causing organisms are present). Higher turbidity levels are often associated with higher levels of disease-causing microorganisms such as viruses, parasites and some bacteria. These organisms can cause symptoms such as nausea, cramps, diarrhea, and associated headaches. Soil runoff
Viruses (enteric)
zero TT Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste

Table 1. List of regulated contaminants in drinking water