The Best Method to Treat Surface Water - Lakes and Ponds

The Best Method to Treat Surface Water - Lakes and Ponds
By Mark Timmons
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The Best Method to Treat Surface Water - Lakes and Ponds

Let's cut right to the chase. If you have read any of my past articles during the nearly 20 years I have written this blog, you might know one thing: I am not a big fan of chlorine. There are a few reasons:

  • It is hard to keep the correct concentration of chlorine as it degrades rapidly;
  • The "point-of-injection" can crystallize and necessitate cleaning the injection fitting (not hard, but it takes time); and
  • Chlorine combines with organics in the water and forms carcinogenic disinfection by-products (DBP's) like trihalomethane (THM) - and that is the prime reason I dislike chlorine.

That said, I would not even think about using anything but chlorine to treat and lake, pond or surface water supply. Why? Because there is not another process that works as efficiently and economically as chlorination! Chlorine is a good disinfectant and disinfection is certainly needed with any surface water supply, as it can contain harmful bacteria, such as e-coli, giardia, and cryptosporidium. Combining chlorination and other sub-micron filtration rids the water of these substances.

Additionally, most surface water contains algae (at least seasonally) and chlorine is one tried and proven method of killing it. Prolonged contact and continuous feeding of chlorine is the ONLY tried and true method of treating surface water. Just because you are using chlorine, does not mean there are disinfection by-products in your water supply. You see, we take out the excess chlorine and DBPs with prolonged contact with Coconut Shell Granular Activated Carbon GAC) so that after treatment, the water is both bacterially and chemically pure. The chlorine and many other chemicals that are potentially present are gone, as well as the bacteria.

I had a gentleman last week tell me that he was disappointed I recommend chlorine for the "makeup water " for his coy pond, as well as his homes water supply. He was upset because he didn't want to use chlorine. He would have been more upset if I hadn't recommended it. Some people have tried hydrogen peroxide H2O2) and I admit that I too have tried that, I am a big fan of H2O2 Technology... except in pond or surface water treatment.

You see, H2O2 is a great oxidizer, but not a good disinfectant. Chlorine is a great disinfectant, but not a good oxidizer. Hydrogen peroxide works well when you use it as an oxidizer, like iron and sulfur removal. You have to use chlorine on surface water, no ifs, ands or buts! Technically, you could also use ozone, but at an astronomical cost: 3 or 4 times more than chlorine for a properly-sized system and even that is problematic.

The gentleman I mentioned above was concerned that chlorine would be able to get into his coy pond. NOT TRUE! The chlorine is consumed in the process and the residual is removed with prolonged contact carbon filtration. No chlorine will be present in the water supply. A typical Chlorination System for surface water might look like this:

From left to right, you have the Proportional Injection System above the White Chlorine Storage Tank that is where you mix the chlorine with water). Next, you have the Retention/Contact Tank or Tanks, followed by one or two depending upon the system) Backwashing Carbon Filters. Finally, there are Two Post-Filters and in many cases, an Ultraviolet Light just for bacterial redundancy.

Surface water can be site-specific, so if your lake or pond is fed by a spring or well, you may need a Water Softener or Iron Filter. In some cases, excessive sand, sit or sediment necessitates the use of a Backwashing Sediment Filter and if you have tannin, you may want to consider utilizing a Pulsr Disrupter Cartridge.

One final word of advice: Since "prolonged contact" is so important in killing bacteria as well as removing the chlorine, it is always better to go a little too big, than too small. Write that one down. Remember, after 45+ years of doing this (and making a lot of mistakes along the way), The (Water) Doctor knows best!

July 28, 2019
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