How Long Can You Leave Water in a Pool?

People don’t like to hear that they need to drain their pool water. Who could blame them? A lot of regions have droughts. It is inconvenient to have to drain your water. It costs money, even if you do it yourself, you still have to pay for the water. Which is not quite as expensive as you think. I have customers with 35,000 gallon pools who paid about $250 for their water. The trick is to notify the water company first so that they don’t fine or re-tier you. You will also want to make sure you are not in a high water table so our pool doesn’t pop out and go sailing down the road.

There are a few ways you can drain your pool water. You can rent a submersible pump from a hardware store. You can hire a professional company to do the dirty work of draining. Reverse osmosis is another way. A truck comes to your home and runs all of your pool water through it and replaces it back in your vessel. This is the “greenest” way. It is also the most expensive way. NEVER, never drain your pool through your filter. Sure, it's great for backwashing a couple of inches, but not the entire pool. You couldn’t drain all the way down anyway. You would be pushing thousands of gallons the wrong direction through your filter and could ruin it.

Hold on! Before you fill that bad boy back up no matter how you drained it, you may want to discuss as a family what other things you may want done while it is empty. You may want an acid or chlorine wash. You may want to paint it. You may want to change lights–things like that.

People who maintain poor water chemistry need to drain their pool around every 3-5 years. People with great water chemistry need to drain it every 5-7 years. Just to average it out, pool water should be completely drained every 5 years. Or, when certain levels get too high. When certain levels get too high that are only resolved by draining we can do a partial or full drain. If you are nearing that 5 year mark, you might as well just drain the whole thing. What levels is this crazy girl talking about? Let’s dive in! See what I did there? I made a pool joke. Ha!

High Total Dissolved Solids

When we add a chemical to our pools, it only breaks down to a certain molecular level. What is left over, are called dissolved solids. The sum measurement of such solids are called Total Dissolved Solids. Why is this an issue? Think of it about the act of dumping sugar in a glass of iced tea. You can keep dumping and dumping, but eventually, the sugar won’t dissolve because there just isn’t enough room! The same thing happens to your pool chemicals. They literally exhaust themselves trying to dissolve, rendering them less effective. To what degree are they less effective? We just don’t have any way to measure, so it’s better to be on the safe side. Anything over 2,500 ppm is considered high.  Anything over 3,500ppm is considered dangerous. Anything over 4,000 is dangerous and the pool should be shut down until a drain can occur. Now I am not talking about a salt pool, just a traditionally chlorinated or brominated body of water. Speaking of Salt …

High Salt Levels

Nearly ALL of my salt pool customers learned this lesson the hard way. Never, never add salt unless you are absolutely sure you need salt. Do not thrush your board readings. Those can go askew due to technology issues or just needing regular maintenance. Did you know when your cell says “low salt” about 70% of the time the cell just needs to be cleaned? I have had many customers end up with salt levels over 5,000 ppm because they just kept dumping to get that pesky light off. Always use a calibrated digital salinity meter or bring your water to a local pool store to have the salt tested prior to adding any salt.

High salt is not good for the salt system. It is not good for your pool’s plumbing or your pool’s surface. It is especially not good for your swimming pool equipment. You see, salt is corrosive. Having extra amounts of salt will corrode your pool in quite a short bit of time. We don’t want to have to spend 4k on a heater unnecessarily, right? Follow your salt system’s instruction book for your ideal salt range for your system.

High Cyanuric Acid

Cyanuric acid is a great product. It helps prevent our chlorine from burning off in a matter of hours. The ideal range for a traditionally chlorinated pool is 30-50 ppm. Of course this is going to creep up over time, but the goal is to have it creep up slowly so that once it is too high, it is time to drain your pool anyway. Many products, like tablets, contain cyanuric acid (CYA). We would never want to use a chlorine, like di-chor, that also has CYA in it in conjunction with our tablets. No, no. 

I have learned two methods that I am going to share with you over my pool career. They both seem to work.  You can either

  1. Float one tablet per 10,000 gallons of water all year round or
  2. You can load up that tab floater in the hot months to allow yourself more surface area and then once the water gets below 70 degrees, take the floater out. Your weekly addition of chlorine will be enough to carry you through each week.

Salt pools don’t have the weekly addition of cyanuric acid so we recommend a 40-50 ppm.

When cyanuric acid gets too high, over 100 ppm, we start to see problems. The chlorine has to fight to do its job, rendering it less efficient. To what degree cannot be measured. So, to keep you and your family safe, it is recommended to drain high CYA. 

Calcium Hardness

Yet another thing that could cause premature draining. Calcium is a naturally occurring element of water and too low of a calcium level, say…under 200, will cause your water to leach it out of your plaster, plumbing, equipment and even you. This can cause etching and other nasty side effects on our plumbing and equipment. On the other hand, too high a calcium level, say over 400 ppm and you start to experience problems. Calcium likes to build up on spillways, water features, in your plumbing and equipment. But wait! Don’t go yet! Make sure to test your hose water’s calcium level. You may just live in an area with high calcium so it would be silly to drain for high calcium, only to put the calcium right back in. Preventing scale-formation can be controlled by several over the counter products. Keeping our pH and alkalinity in range will also be a good advocate for your pool’s calcium build up.