Understanding tap water parameters from local water reports

Introduction

The quality of your tap water can have a big impact on your planted aquarium. For people who are not armed with an assortment of test kits to test every parameter, reading the local tap water report can give a good indication of what is in your water. Knowing what is in your tap water can make a big difference to the decisions you make when setting up your aquarium. For example, if your tap water is very alkaline with high carbonate hardness, you may want to avoid plant species that require very soft water to thrive. Similarly, if your tap water is super soft with low calcium and magnesium levels, you may want to consider raising these levels with a GH booster if you are growing plants that prefer higher calcium and magnesium levels.

What do the columns and units mean?

Here we use a drinking water report from Singapore. In the leftmost column we see the parameters listed. Many of the parameters listed are compounds associated with environmental pollution. If your tap water is safe for human consumption and cooking, these levels should be in the safe zone for fish/plant tanks. Most of the long list of parameters have no effect on our tanks and can be ignored. We will discuss which parameters are important below.

The second column, the Unit column, tells us what units the rest of the numbers are in for that particular row. There are two main notations that we use for the parameters that are important to us; ppm and ppb. ppm means parts per million, 3ppm means that in 1 million units of tap water mass there will be 3 units of that particular element. mg/L is the same as ppm as far as hobbyists are concerned. ppb means parts per billion and is the same as (ug/L), 5 ppb means that there are 5 units of that particular element in 1 billion units of water mass. ppb or ug/L is generally used for very toxic contaminants where standards for tap water contain dictate that only an extremely tiny amount is allowed in tap water.

Columns 3 and 4 give guidelines from health organisations on the maximum acceptable limits for each parameter in question. These guidelines may come from the World Health Organisation or other ministries of health. It's common to find WHO standards listed in most water reports. If there is no value listed, it means that health organisations have no prescribed maximum limit for that particular parameter. These columns are there so that people can check the levels in their tap water against the recommended limits. If the tap water is drinkable, one would expect each parameter to be within the limits set by health organisations.

In this water report, columns 5 and 6 give the value of the parameters. These are the 2 columns that give us the data we are interested in. In this water report, they are detailed and give both average values and the possible ranges of parameters. In other water reports you may find only one value, the average, listed.

For example, the table above shows TDS (Total Dissolved Solids). The unit for TDS is mg/L, which is the same as ppm. Columns 3 and 4 are blank as the WHO has no guidelines for this particular value. The mean value is given as 107 mg/L, with a range of 62 to 250 mg/L. The range is quite wide in this situation: the TDS value can vary considerably from one household to the next.

The New York City water quality report. Note that columns 2 and 3 are not the measured values; they are the maximum allowable values given by the health authorities. The actual water parameters are in columns 5 and 6, which give the range and average values respectively. If we look at copper, the maximum allowable level in tap water is 1.3ppm (columns 2 and 3), but New York's tap water contains on average only 0.007ppm of copper (column 6).

If we look at the value for hardness (CaCO3), the range (column 5) is actually very, very wide, from 16 to 106. This corresponds to an alkalinity of 1 dKH to about 6 dKH. Depending on your area, you may be able to keep very soft water plants without problems (if your dKH is 2 or less), or the water may be too alkaline (if it is at 6dKH). This is where the range is important - you will only know where you fall in the range if you test your own tap water.

Which values matter where planted tanks are concerned ?

For a detailed break down of what each parameter means and why, there is much more details in our other articles here. 

pH - This value is much less important than people think; it is the underlying KH value that is more important - pH tends to anchor close to KH values, but it is also a value that can move over a wide range when KH is low. It also changes a lot once it enters the tank. My tap water comes out at around pH 7.6, but drops to around pH 6.4 after sitting in the tank for a while. To know if you can really keep soft water fish/plants you need to check the carbonate hardness (KH), pH is too rough a measure. KH levels remain stable unless you specifically introduce means to change them. KH should be the parameter people focus on when considering alkalinity or hardness issues, but pH values can indicate that you have hard water, for example if they are significantly higher than 8.0. In general, if tap water has a pH below 7, it is usually due to dissolved carbon dioxide. Most governments add additives to stabilise the pH around neutral to prevent erosion of metal pipes.

To read more on why pH matters or not, head here.

TDS (Total Dissolved Solids) - Again, this is a popular figure, but it is much less important than people think. What makes up the TDS is much more important than the total. This TDS value does not tell you what is dissolved in the water. For example, if you have tap water that is 15ppm, you might interpret that as great tap water, but if it contains 5ppm of copper, that would be lethal to all aquatic life. Similarly, if the tap water has 200ppm TDS, but it is mostly calcium and other benign elements, the tap water may be ideal for aquatic plants. As a very general rule, if your TDS is below 100ppm, you almost always have very soft water. As the TDS rises towards 300ppm and above, this is usually due to water coming from limestone areas - meaning that you usually have hard water. To know exactly how hard we need to look at other parameters such as carbonate hardness or KH. To read more on TDS click here.

 Chlorine/Chloramine - In countries where tap water has low levels of chlorine, it can be mistaken that a dechlorinator is not required when water changes are made. This works when smaller water changes (e.g. 10-20%) are made, as the effects of chlorine may not be apparent (at least immediately) due to dilution. This combination is probably what gave rise to the myth that you should not change all the water in the tank at once (100% water changes). Chlorine kills the micro-fauna in the tank and damages the gills and skin of the fish. If your tap water contains chlorine, you should definitely use a dechlorinator, then you can change as much water as you like. Large water changes generally result in cleaner tanks, less accumulated organic waste particles and are beneficial for tanks with algae problems. It is common for tap water to have chlorine levels between 0.5 and 2.5ppm, with some outlying areas having even higher levels.

Hardness (CaCO3) - This is often given in ppm rather than dH, so you will need to use an online converter or divide the ppm value roughly by 17 to get the hardness reading in degrees. For very soft water plants such as Syngonanthus and some finicky Eriocaulons, you would look for a value below 2 dKH (or 35ppm) under Carbonates. Most plants will do well in moderately hard water up to 10+ dKH. However, as you approach 16dKH and beyond, an increasing number of plants will grow less optimally. On the other hand, there is no minimum requirement; almost any hard water plant can grow well in soft water, but the reverse is not true. 

For a more detailed breakdown of water hardness, read the links on this page. There is no easy way to reduce water hardness except to install an RO system. 

NPK (Nitrate, Phosphate, Potassium) - These are often present in small amounts in tap water. This allows us to adjust our fertiliser dosage in cases where the level is extremely high. For example, if your tap water has 15ppm nitrates and 4ppm phosphates, you can probably dose a liquid fertiliser that has less or no nitrates/phosphates. There is no easy way to remove NPK from tap water except by using an RO filter.

Copper - In some cities there may be copper in the tap water. You will quickly know if it is present in significant quantities as copper is lethal to aquatic life, especially invertebrates such as shrimp. Depending on the species, 0.1ppm or less of copper can be lethal. The use of dechlorinators containing chelating agents that bind such heavy metals can alleviate copper toxicity in less severe cases. RO water is recommended to eliminate significant amounts of copper.

Calcium - Most tap water contains at least some calcium. Shrimp and certain hard water plants prefer higher calcium levels. If your tap water is super soft, with less than 30ppm calcium, it definitely helps to raise the calcium level to 40-60ppm using GH boosters/remineralisers. Plants such as Rotala Florida and Cryptocoryne flamingo fall into this category. There is no real downside to having higher calcium levels until they reach extreme levels.

Rotala florida and Cryptocoryne flamingo are two popular plants that grow faster, with less melting issues in water with higher Calcium values.

Magnesium - Magnesium is a macro-nutrient that is often under-represented in aquarium fertiliser science. Especially for faster growing tanks, tap water often does not contain enough Magnesium for the needs of the tank. Some picker species such as Rotala macrandra prefer higher magnesium levels in the water column. If your tap water has less than 5ppm or so of Magnesium, it is helpful to increase its levels to 10+ppm with a GH booster containing Magnesium.

Conclusions

Far too many people pay attention to the unimportant variables such as TDS and pH, while ignoring critical parameters such as carbonate hardness (KH), calcium and magnesium levels. Tap Water Reports are an easy way to find out what is in your tap water without having to invest in a full range of test kits. It is useful for spotting any outliers in parameters that can affect your aquarium maintenance. It is generally easier to work with your tap water than against it - so if you have more alkaline tap water, avoid soft water plants. If your tap water doesn't have ideal parameters, don't try to add things like buffers and acids to get to a target parameter. Do not add to take away. There is always Reverse Osmosis (RO) water for those aquarists who want to start with a clean slate to grow any type of plant in their tanks. For most, it's best to choose plants and fish that work with your water rather than fiddling with the parameters.

At our gallery, we have super soft tap water that comes out of the tap with less than 1 dKH. We also have low Calcium and Magnesium values, so we do add a water remineralizer to raise Calcium and Magnesium values.