Preventing Algae From Building up in Water Tank 1

[CWEngineer]

In a small town in Mexico it is common to use water tanks (about 50 gallons) on top of the roof of the houses to provide water throughout the house. I believe this is done to increase the water pressure and to have water available when there is no water due to line breaks, among other things.

We are planning to install a tank (I believe its about 300 gallons) for a bigger house. We are forseeing that algae will build up in the tank (specially if we are using the house as a vacation home and there is not much movement in the water).

I guess here goes my questions:
1. Do you guys have any recommendations to prevent algae from forming in the tank? The water is intended to be used for all purposes.
2. Do you guys know of any available literature online that I can read up on?

THANKS FOR YOUR HELP

 

[sbush]

I visited Merida this summer and I saw the tanks you are writing about.

Most of the common types of algae require light to survive (i.e., photosynthesis). Therefore, the best way to prevent growth is to reduce or eliminate the light that can enter the tank.

You should begin by using an opaque tank. I suggest the all black polyethylene type, as opposed to the milky white translucent type.

Since this tank will drain by gravity, you must have an adequately sized vent. This becomes another potential source for light to enter the tank. Instead of the usual "mushroom" vent that is typically molded into the cover of these tanks, I would completely seal the cover and install a threaded fitting (typically called a "bulkhead") in the top of the tank at the highest point available. Then I would pipe away from the vent, using opaque PVC pipe, and run the piping over the side of the tank so that it also functions as an overflow. The end of the vent pipe should be screened to prevent pests and insects from entering. Remember to oversize the vent pipe opening to account for the loss of open area caused by adding the screen.

The inlet connection (and any other tank penetrations)should be made by a tightly threaded joint similar to the bulkhead coupling method. Do not cut a hole and run a pipe through the bore of the hole, as light can enter through the tolerance between the hole and the pipe wall.

If you keep the light out of the tank, you shouldn't have any algae problems. But, if you desire to spend a lot more money, you could also consider installing a properly sized ultraviolet light inside the tank. Be sure to contact a professional for sizing and installing the UV light. One size does not fit all...and electricity in water is always potentially dangerous.

Good luck.

S. Bush

http://www.water-eg.com

 

[PUMPDESIGNER]

sbush did a good job, all that is left to me is to confirm what he said. Algae cannot grow without light being a photosynthesizer.

The HDPE tanks cannot be painted, paint will not stick to them. Find some other method to cover the tank remembering that there is hardly any adhesive that will stick to HDPE. 3M makes two adhesives that stick to HDPE pretty good but not great (9471LE and 300LSE), but those are hard to obtain usually.

Best build something around the tank to cut off light completely.

Also, it would be better to cover that tank with a white painted cover to reflext light, dark colors will heat the water much more than reflective covers. If you put a wood cover over the tank paint that wood white, and then make a fancy vent system for the cover (torturous path) to prevent entry of light but you must vent to allow hot air to escape.

PUMPDESIGNER

 

[hydrae]

While removing the light will stop the growth of algae, it will not prevent the growth of bacteria, protozoon’s, and viruses. Do you know the quality of the water supplied, and is it intended to be consumed?
If it is to be consumed and if it a surface water and treated to meet EPA standards, I would recommend exchanging the volume at least once to week to maintain the residual, if the source is ground water it can last longer but will still require fresh supply on a regular basis. The test there is the disinfectant residual, when the residual drops below detection (0.2 mg/l) replacement is required. If it stays below detection too long the tank will become contaminated and a cleaning with disinfection is required. Testing with a swimming pool DPD test kit will tell you the disinfection level. Mexico is warm and humid in most locations, so the time frame I list may be too long, in any case the provisions mentioned by pumpdesigner for keeping the water cool is a must.
Also regular cleaning of the tank is a must.
Since you are not there, a timer, solenoid valve, and overflow can do the trick of keeping the water fresh.
If it not to be consumed or consumed only after boiling, then algae control as described by sbush and pumpdesigner are adequate.

The tanks do not increase water pressure, in fact it will lower the pressure to a value equal to the level the tank is at, but it may seem to be more pressure because the line losses are significatly reduced between the source and use.

Hydrae

 

[CWEngineer]

Thanks for the information it has been very helpful.

I believe we are now changing our plans to put the approximate 500 gallong tank underground - so light should not be a problem.

The water is intended for drinking water.

Do you guys forsee any problems with the water that might occur say in 3 months, 6 months, 1 year, etc.

I am doing research on methods to test water and treat it. I would really appreciate it if you guys could advice me on some inexpensive methods that I can use to test and treat the water?

thanks

 

[hydrae]

gman1

With a 3 month (or longer) time frame between uses, I would clean, disinfect, and refill the tank on every arrival (unless you have a filling device that automaticly replaces the water on a regular basis). On departure I would drain and seal the tank to make cleaning easier on arrival. Since you are looking at installing below ground you should consider the reliability of the power grid, since now power is required for normal water use. The reason the other tanks are on top of the buildings to provide water when the water system is off regardless of whether the power is on or off.

As for Treatment
Find out the existing source and treatment to determine what to do for your own protection. As a minimum verification of a residual is cheap and easy using a DPD test kit (if they disinfect)

Hydrae

 

[sorghumco]

gman1
i am new to the discussion. it has been helpful. i am planning to buy a plastic water tank for irrigating our garden. preventing algae growth is important. the readily available tanks in my area are white or light green (agricultural/rural usage). is the light green tank opaque enough to prevent algae growth?
the black water tanks: would the water heat up too high for direct irrigation? (we are in northern missouri).

thanks,