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Thread: How often do they change pool water completely?

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    Very Active Member ddl's Avatar
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    How often do they change pool water completely?

    Anyone knows how public swimming pools are maintained? Do they completely change the pool water at the end of day, or weekly? Anything they do to the pool overnight (just circulate like daytime, or do nothing, or change entire pool water)? Is the water cleaner in early morning than evening because of this? Thanks.

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    Very Fetching Rump SwimStud's Avatar
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    Re: How often do they change pool water completely?

    Quote Originally Posted by ddl View Post
    Anyone knows how public swimming pools are maintained? Do they completely change the pool water at the end of day, or weekly? Anything they do to the pool overnight (just circulate like daytime, or do nothing, or change entire pool water)? Is the water cleaner in early morning than evening because of this? Thanks.
    I think our Y is every other year.



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    Very Active Member Seagurl51's Avatar
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    Re: How often do they change pool water completely?

    Most pools, I think, are only drained completely once or twice a year. Pools I've worked at have crews come in and night and vaccuum the entire pool, or the lifeguards put in an automated little robot who does it. It kind of depends on if the pool is indoor or outdoor and what it's used for. Chemicals (chlorine levels, etc) are always checked at least twice a day though in any pool regardless of location or primary function.

    I'd say the pool is the same amount of clean all day. Maybe a little more so in the morning simply because people haven't been in it for a few hours.

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    Re: How often do they change pool water completely?

    I just sent an email to and called the Evanston health department about the local LA Fitness pool. I'm convinced they have no idea how to maintain the damn thing. I doubt it's clean in the morning or the evening. I'm never going back there again. (PM me if you want details.)

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    Re: How often do they change pool water completely?

    I know that at my school, we check the water every hour. I believe that is NY State law. We change the water twice a year. The board of health comes around periodically to check our logs.

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    Re: How often do they change pool water completely?

    at my Y, it is changed once a year. But, they are a little lazy on putting fresh water in the pool and thus, the pool gets extremely cloudy.

    At Villanova, it is probably changed sometime in the summer. All I know whether they change or not, it is a very clean pool. Sometimes, the pool temperature is higher and it gets foggy above the water.

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    Active Member alphadog's Avatar
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    Re: How often do they change pool water completely?

    I moved to Colorado from Houston 10 years ago and was amazed that they drain pools in Colorado...ever. I was a swimmer and lifeguard in Houston for over a decade and I don't remember anyone ever draining a pool except for major maintenance. It certainly wasn't routine. I could be wrong, but I think you could theoretically maintain a pool without draining it forever if you had the right chemical balance, filtration, and debris removal. I believe good filtration systems filter the entire volume of a pool every couple of hours. Every pool needs "fresh" water to replace what evaporates or is splashed out.

    I would contend that most pools are about the cleanest place you'll subject yourself to in a given day (consider what's on a bathroom doorknob), if we're talking about germs. It always cracks me up when they close a gigantic pool for 24 hours because some kid puked or had an accident. With the chlorine and pH levels in most pools, I don't believe there is any real danger after a few minutes, especially when they scoop some more chlorine in the affected area. From a former lifeguard's perspective, we always loved it when that happened because we got out of work for the day.

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    Very Active Member mermaid's Avatar
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    Re: How often do they change pool water completely?

    Typically, pools are not drained completely unless there are major renovations or maintenance demands. There simply is no need to do that.

    Fresh water is added to the pools - either manually or through an auto-fill system - either directly into the pool or in the pump room. Water is loosed through evaporation, pool activities and routine cleaning of the filtration system (backwashing). Occasionally, fresh water will need to be added (after pool water is "dumped") because of an extreme chemical imbalance. In this case, the pool should be closed and you probably will not know about it.

    There is a number of reasons pool water turns "white cloudy" (low turbidity). Improper filtration, insufficient water circulation or flow rate, poor water chemistry, wind, rain, vegetation, dry skin flakes, cosmetics and hair products from swimmers are among the many factors that need to be examined. In short, cloudy water is the result of microscopic suspended particles. Determining the contributing factor will yield the proper remedy.

    If the pool water turn colors like blue-green or red-brown, then you have a more serious condition and should have an expert examine the situation.

    Pool water temps. in relation to air temp.: The most ideal is to have the air temp 5 degrees warmer than the water. This is not always possible. At a minimum, air flow/ventilation is absolutely necessary.

    Recreational water illnesses are caused by cryptosporidium (parasite), Giardia (parasite), E. coli (bacteria) and shigella. When people infected with these diseases have a fecal release in the water and there is insufficient disinfectant (most often Cl) to inactivate the pathogen, then swimmers who ingest water, will swallow some of those germs and will become ill. Crypto can remain active at normal disinfectant levels for several days (6 -7 days). Protozoa are resistant to chlorination in swimming pool water.

    Therefore, remedies for total disinfection are to raise the Cl (or sanitizer) level to an unsafe swimming level and allow the pool water to turn over (filter) and return to an accepted level. The flow rate (turnover rate) at your pool will determine the length of time this process will take.

    In most areas, at a minimum, the Health Department regulates pools by taking weekly water samples and yearly visits. If there is a problem cited or water tests reveal a potential hazard, the Health Department is obligated to intervene and possibly fine ($$) or close a pool until the problem(s) are resolved.

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    Re: How often do they change pool water completely?

    I lifeguarded and maintained pools for about six years beginning in high school and through most of college. I worked at community pools, a country club pool, and several pools at an Air Force base in San Antonio.

    We never drained the pools. Water wasn't expensive then but it is now.

    In my experience water quality was always best in the morning unless circulation was turned off overnight. I haven't been in a "public" pool that had filtration to keep a pool crystal clear throughout a day when people were in it. But overnight the filters catch everything because nothing new is being introduced into the pool.

    People bring dirt into pools. Sweat, skin flakes, suntan oil, etc.

    Chlorine breaks down in the sun - so chorine use is much higher during the day for an outdoor pool. We occasionally forgot to turn the chlorine down (when we had a chlorinator) at the end of the day. The result was very high chlorine levels in the morning. Chlorine doesn't work as well when the ph is wrong - so the chemical balance is important.

    Filters also need to be cleaned or backwashed (reverse the direction of water flow to rinse dirt out of the filter media (like sand).

    Algae grows too - and is usually taken care of with more chlorine. The algae is killed, but needs to be physically removed from the pool via vacuum or the filters (not effective because the dead algae settles on the bottom).

    I don't think there is any excuse for frequently cloudy water. Pools will not be crystal clear all the time but the water should be appealing most of the time.
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    Very Active Member ddl's Avatar
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    Re: How often do they change pool water completely?

    Thanks to the replies! That is so informative! I had thought they drain the pool every day, or at least every week! How laughable! Though in theory one could catch disease from a public pool, I haven't heard of real instance yet, so maybe most pool are ok... Whatever, we have no choice...

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    Bigger than a breadbox mattson's Avatar
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    Re: How often do they change pool water completely?

    One thing they do in Europe that we don't have in the US is walking through a foot-pool before going on deck. I have to image that simple step (especially after visiting the rest room!) would help keep the water clean.

    (Too bad the heavy perfume/cologne people forget about the "take a shower before entering the pool".)

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    Re: How often do they change pool water completely?

    most pools lose enough water through splashes, people and evaporation that they're being refilled pretty regularly. now that is probably only a couple hundred or couple thousand fresh gallons being added at a time, but it indeed does help. some places do this automatically; others you have to manually turn on the fill spout near the diving well.

    Pools are generally a bit clearer every morning for the sheer fact that they've been sitting for several hours with no (or if outdoor, few) impurities entering, and the filters have had a nice chunk of time to turn the water over.
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    Re: How often do they change pool water completely?

    Just re-confirming what everyone has already said. At the pool I spend most of my time at (Blodgett Pool at Harvard), I think our filters circulate the entire pool every 5 hours +/- based on circulation flow rate. In a large pool such as ours, water is being added very regularly. Not sure how long it takes us to add a full 750,000 gallons of new water, though.

    For us, one of the biggest problems with cloudy water is simply air bubbles. Sometimes if there is a leak in the circulation system, air can leak into the pipes, and cause really small air bubbles in the water, which makes it cloudy.

    Also everything else... dirt, grime, hair product, lotion, etc., that comes off of everyone. (There is a good reason they ask you to shower first!)

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    Very Active Member david.margrave's Avatar
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    Re: How often do they change pool water completely?

    The pool I learned at (Grizzly Pool in Missoula, MT) had a foot pool as you exited the locker room onto the pool deck. They rarely filled it though, and I think they may have taken it out altogether when they renovated the pool at some point. I don't think I have ever seen that at any other pool, now that I think of it.


    Quote Originally Posted by mattson View Post
    One thing they do in Europe that we don't have in the US is walking through a foot-pool before going on deck. I have to image that simple step (especially after visiting the rest room!) would help keep the water clean.

    (Too bad the heavy perfume/cologne people forget about the "take a shower before entering the pool".)

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    Very Active Member moodyrichardson's Avatar
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    Re: How often do they change pool water completely?

    This year, TN has required all pools to be inspected by the health dept., the same as restaurants. They are also required to post their scores for public view. The university, where I work, drains twice yearly I think. They test the water every 1/2 hour. Their pools are always well maintained. Now the public outdoor pool in the town, where I live, is a much different story....

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    Re: How often do they change pool water completely?

    Mermaid, Hoffman, Blackbeard, and Osterber nailed it. The only things I would add are: 1. Where I live, there are a number of fitness facility pools that the department of health requires to have the water at 82 degrees. 2. Early morning (4-5am) swimmers seem to experience the clearest water of the day, since it is easier for pool techs to work when the pool is least used. Getting a proper ph balance is said to be a pain and even far more difficult when there are people in the water. Therefore a lot of techs work at night. However, also note that the ph levels can be too high in the early a.m. and left at those levels with the mindset that swimmers and noodlers will have those levels down to proper levels by e.g. 9am which will be perfect for potential inspection times. 3. Even if every aforementioned preventative measure is taken, you are still at risk for Crypto. While I was living in Vegas last year, the Salt Lake County in Utah had a county-wide outbreak. At large pools with a lot of kids, they now have everyone exit the pool for ten minutes every hour so that they can test for Crypto and so that parents can change swim-diapers and take their children to the bathroom. I do not swim in any of those pools, though at least one of them was a USMS training pool

    (Side note: You never fully realize how much chemicals are in pool water until you swim in open water. It amazes me every time. I also prefer the pool water that is run through a salt filtration system vs a sand filtration system. The chemicals seems less harsh.)
    Last edited by mikedilv; September 16th, 2008 at 09:34 AM.

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    Re: How often do they change pool water completely?

    I have never heard of a salt based filter. I don't see how that would work. But maybe I'm just not keeping up.

    I'm most familiar with sand, DE (diatomaceous earth), and cartridge filters (usually in home pools).
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    Very Active Member mermaid's Avatar
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    Re: How often do they change pool water completely?

    I think what mikedivl meant to say was Salt Cell System - not salt filtration system.

    hofffam - you are correct there are an assortment of Sand, DE, and Cartridge filtration systems.

    A Salt Cell System takes salt water (NaCl), passes it over electrically charged plates (in a process called electrolysis) to release the chlorine in the salt. NaCl in and HOCl out. Although chlorine is not used per se, chlorine is still present.

    Yes, pools with Salt Cell Systems have water that is much "softer" and "easier" on the skin. Over time, Salt Cell Systems save money too.

    The pH is the key to skin irritation -- too high or too low and you will have issues. The pH of your eyes is approx 7.4 - 7.6 (a greater population on the higher side). That is why the swimming pool guidelines have been established as such. For the ease and comfort of your body (& parts).

    Regarding the water temp -- the activities taking place in the pool will dictate the temperature more than the local ordinance in most jurisdictions.
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    Re: How often do they change pool water completely?

    Ah, salt "cell" system. Thank you for correcting me. I used to swim in a pool at 24hr Fitness that had that system. Whenever water would get in my nasal passages or at the back of my throat, it was really quite tolerable. Now that I swim in two other pools that don't have the salt cell system, I notice the water seems more acidic and less tolerable. I know, don't inhale the water

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