The quality of tap water can have a great impact on planted tanks. For folks that are not imbued with an assortment of test kits to test every parameter, reading the local tap water report can give good clues as to what is in your water. Knowing what is in your tap water can greatly change the decisions you make when setting up your tank. For example, if your tap water is very alkaline with high carbonate hardness, you might 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 might consider raising those levels with a GH booster when growing plants that prefer higher Calcium and Magnesium values.
Here we use a drinking water report from Singapore. On the left most column we see the parameters being listed. A large number of parameters listed are compounds associated with environmental pollution. If your tap water is safe for human consumption and cooking, those values should be in the safe zone for fish/planted tanks. Most of the long list of parameters have no impact on our tanks and can be ignored. We will cover more on what parameters matter below.
In the second column, the Unit column, tells us the units that the rest of the numbers are in for that particular row. There are two main notations that we use for the parameters that matter 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 hobbyist usage is concerned. ppb means Parts Per Billion and same as (ug/L), 5 ppb means that in 1 billion units of water mass, 5 units is of that particular element exists. ppb or ug/L is generally used for very toxic pollutants, where standards for tap water contain dictate that only an extremely tiny amount is permitted in tap water.
Columns 3 and 4 includes guidelines from health organizations about the max permissible limits for each parameter in question. These guidelines may be from the World Health Organization or other health ministries. It is common to find WHO's standards listed in most water reports. If there is no value listed, it means that health organizations do not have a prescribed maximum limit for that particular parameter. These columns are present so that citizens can check values in their tap water against the recommended limits. If the tap water is drinkable, one would expect every parameter to be within the health organizations prescribed limits.
In this water report, columns 5 and 6 gives the value of 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 just find one value, the Average, being listed.
Let us look at an example; in the above table, the TDS (Total Dissolved Solids) is listed. The unit for TDS is mg/L which is the same as ppm. Columns 3 and 4 are empty, as WHO has no guidelines for this particular value. The Average value is listed as 107 mg/L, with the range being from 62 to 250mg/L. The range is quite wide in this situation: the TDS value can vary significantly from one household to the next.
The water quality report from New York city. Note that columns 2 and 3 are not the readings; they are values for the maximum permissible amount given by health authorities. The actual water parameters at at columns 5 and 6, which gives the range and average values respectively. If we look up Copper; the maximum permissible amount in tap water is 1.3ppm (columns 2 and 3); however, New York's tap water only contains 0.007ppm of Copper on average (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 translates to 1 dKH to around 6 dKH of alkalinity. Depending on your area, you might be able to keep very softwater plants without issues (if your dKH is 2 or less), or the water could be too alkaline (if its at 6dKH). This is where paying attention to the range is important - you will only know where you fall within the range if you test your own tap water unfortunately.
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 matters a lot less than what people think; it is the underlying value of KH that carries more importance - pH tends to anchor close to KH values, but it is also a value that can move within a large range if KH is low. This value 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 some time. To know whether you can truly keep soft water fish/plants, you need to check the carbonate hardness value (KH); pH is too rough a gauge. KH values stay stable unless one specifically introduces means to alter it. KH should be the parameter people focus on when pondering over questions of alkalinity or hardness. pH values may hint that you have hard water though, for example, if the values are significantly higher than 8.0. Generally, if tap water has a pH below 7, it is usually because there is carbon dioxide dissolved in it. Most governments add additives to have the pH stabilize around neutral to prevent the erosion of metal piping.
To read more on why pH matters or not, head here.
TDS (Total Dissolved Solids) - Again, this value is popularly quoted but is much less important than people think. What makes up the TDS is much more important than the total value. This TDS value does not tell you what is dissolved in the water. If say you have tap water that is 15ppm, one might interpret that as having great tap water, however, if it contains 5ppm of Copper, that would be lethal to all aquatic life. Similarly, if tap water has 200ppm TDS, but its mostly Calcium and other benign elements; the tap water can be ideal for aquatic plants. As a very general gauge, you almost always have very soft water if your TDS is below 100ppm. As tap TDS rises towards 300ppm and above, it is usually because of water sourced from limestone areas - meaning that usually this means that you have hardwater. To know how hard exactly, we have to look at other parameters such as Carbonate hardness or KH. To read more on TDS head here.
Chlorine/Chloramine - In countries where tap water has only low levels of Chlorine, it can give rise to the illusion that dechlorinator is not required when water changes are done. This works if smaller water changes (such as 10-20%) are done, as due to dilution, chlorine's effects may not be apparent (at least immediately). This combination is also what probably gave rise to the myth that one should not change all the water in the tank at once (100%) water changes. Chlorine nukes the micro-fauna in the tank, and damages the gills and skin of fish. If your tap water contains chlorine, you should definitely use a dechlorinator, then you can change however much water you want. Large water changes generally results in cleaner tanks, less accumulated organic waste particles and are beneficial for tanks facing algae issues. It is generally common to have tap water have chlorine ranges of between 0.5 to 2.5ppm, with some outlier areas having even more.
Hardness (CaCO3) - This may often be quoted in ppm rather than dH so you will need to use an online converter or divide the ppm value by 17 roughly to get the hardness reading in degrees. Very soft water plants such as Syngonanthus and some pickier Eriocaulons, you would look for a value below 2 dKH (or 35ppm) under Carbonates. Most plants do well even in moderately hard water up to 10+ dKH. However as you approach 16dKH and beyond, an increasing number of plants will grow less optimally. There is no minimum required value on the downside; almost every hardwater plant can be grown well in soft water, but the opposite 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 values (Nitrate, Phosphate, Potassium) - These are often present in some small quantities in tap water. It allows us to adjust our fertilizer dosing in cases where the value is extremely high. If your tap has 15ppm of Nitrates and 4ppm of Phosphates for example, you can probably dose a liquid fertilizer 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 present in the tap water. You will know if this is present in significant quantities quickly, 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. Usage of dechlorinators that contain chelating agents that bind such heavy metals can alleviate copper toxicity in less severe cases. To eliminate significant amounts of copper, RO water is recommended.
Calcium - Most tap water contain at least some calcium. Shrimp and certain hard water plants prefer higher calcium values. If your tap water is super soft, with below 30ppm of Calcium, it is definitely helpful to raise Calcium levels to 40-60ppm using GH boosters/remineralizers. Plants such as Rotala Florida and Cryptocoryne flamingo fall into this category. There is no real downside to having higher calcium values 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 aquatic fertilization science. Especially for faster growing tanks, tap water often does not contain enough Magnesium for the tank's needs. 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, boosting its levels with a GH booster that contains Magnesium to 10+ppm is helpful.
Far too many people pay attention to the variables that do not matter significantly such as TDS and pH, while failing to take note of critical parameters such as Carbonate hardness (KH), Calcium and Magnesium values. Tap water reports are an easy way to find out what is in your tap water without the need of investing in a full range of test kits. It is useful for spotting any outliers in parameters that can affect your tank upkeep. Working with your tap water rather than against it is generally easier - so if you have more alkaline tap water, avoid soft water plants. If your tap doesn't have ideal parameters it is best not to try and add things to it like buffers and acids to achieve a target parameter. Do not add to take away. There is always Reverse Osmosis (RO) water for those aquarists that want to start with a clean slate to be able to grow any type of plant in their tanks. For most, it's best to pick plants and fish that work with your water rather than wrestle 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.