Heavy Rains & Swimming Pools

heavy rains and swimming pools

Whether you’re dealing with a summer monsoon or surprise downpour, rainstorms happen year-round and can be a cause for concern among pool owners. If you’re wondering how heavy rains can be problematic for swimming pools, you’re in the right place! While rain might appear pure and clean, it is actually a carrier for contaminants, and can throw off water chemistry.

Excess Water in Your Pool

If you find yourself dealing with inches of precipitation, you may need to lower the water level in your pool to maintain proper skimmer function. Excess water in the pool that reaches the brim can also bring in extra contamination from surrounding planters and deck area flooding during a heavy rain.

For most pools with a sand or D.E. filter, the simplest way to lower the water level is to either backwash the filter or put the multiport valve into the “waste” position, and roll out the backwash hose. If you have a slide (push-pull) valve, backwash the filter to lower the water level. Just make sure you don’t lower the water level too much, or you’ll risk damaging your pump! The water level should stay around halfway up the mouth of the skimmer at all times.

cover pump

Some pools have a hose spigot plumbed after the pump or on the filter valve, which means you can connect a garden hose to lower water level. Alternatively, you can use a submersible pump, aka a pool cover pump, to keep the pool from overflowing.

Finally, there is the siphon method. A pool vacuum hose works best. Prime the hose in the pool to fill it full of water, then attach a vacuum head or use a heavy item to hold the hose on the first or second step or a few rungs down on the pool ladder. Cap the other end of the hose with your palm, and quickly pull the hose away from the pool and a few feet below the level of the pool water. Uncap the hose at ground level and let it flow! Again, keep an eye on it so the water level doesn’t drop too much!

Contaminants in Your Pool

Heavy rains bring all kinds of contaminants into your pool, whether directly from the rain or from runoff caused by flooding. Testing your pool water before and after a rainstorm will help you stay on top of any chemical imbalances that may result in your pool.

From Runoff

clarifier

When a backyard pool gets 5 inches of rain in a few hours, flooding can result. If surrounding planters, lawns, or even concrete pool decks overflow into the pool, just a handful of soil or mulch can elevate phosphate levels and create problems with cloudy water and algae.

In severe cases, a pool can fill with a thick layer of silty mud, and all sorts of debris. Use leaf rakes to remove the big stuff, followed by a slow vacuum to waste. Follow up with a good daily pool brushing, and near-continuous filtering. Clarifiers and flocculants can be used to speed up the process considerably. If you have a sand filter, using these kinds of chemicals may be necessary to improve filtration efficiency and get rid of the finest silt and debris.

As the water clears, use a phosphate remover chemical like PHOSfree or SeaKlear to naturally eliminate phosphates in your pool. Just pour it into balanced pool water, run the filter for 24 hours, then backwash.

From the Rain

super algaecide

Rain is pure, distilled water, but as it falls through the air, it picks up dust, pollen, pollutants, oils, and even algae spores. If you have tall trees overhanging the pool, rain will wash them clean, right into your pool, adding phosphates, algae spores, and other organic gunk. Add algaecide before a storm to help battle incoming invaders as they enter the pool.

Heavy rains can also impact your pool’s water balance, with the greatest impact on the pH and Total Alkalinity. Acid rain falling through smoggy summer air hits your pool at a very low pH, reducing pool pH and Total Alkalinity. Be sure to test your water with a complete test kit, then balance as needed. Imbalanced water can cause all sorts of problems in your pool, including stains and scale, corrosion, and water quality issues like algae and cloudy water.

Wind & Debris

Strong winds during a rainstorm can be vehicles for bringing contaminants and debris into your pool. If the wind is intense enough, anything from garbage to organic material can be picked up and thrown into your pool water.

Before a Storm Hits

Store all loose toys, furniture, and cleaning equipment that could become airborne in high winds. But as tempting as it may be, DON’T cover the pool — the cover can be severely damaged in a heavy storm.

After a Storm Hits

In The Swim Super Pool Shock

Clean the pool, lower the water level to normal operating levels, check the water balance and chlorine level, adding sanitizer if needed. In most cases, we strongly recommend shocking the pool following any contamination event — including storms. If needed, superchlorinate the water with some pool shock, and run the pump to circulate and filter the water.

Most of the time, you’ll need to run the pump for at least 24 hours, or until the water is clear and healthy once again. It’s best to remove leaves and debris from the pool first, and ensure pH levels and other aspects of water chemistry are within the proper range before shocking the pool.

Flooded Pool Equipment 

Keep the pump running unless flood waters threaten to submerge your equipment. In those instances, if you can turn off the power and safely remove the pump, store it indoors. Keep in mind that if the pump motor is submerged or becomes waterlogged, it will likely need to be replaced once flood waters recede.

Regular rain falling on your pool equipment will usually not cause any harm, even if it lasts for days. But if you’re concerned, place a cover over your filter pump. Flooding due to heavy rain is the real problem. Sand bagging your pool equipment could save you from replacing the pump or motor if flood waters rise above the equipment pad. If you have any other electrical components, such as a heat pump, salt cell, or other electrically-powered equipment, inspect it thoroughly before restoring power. When in doubt, it never hurts to seek the help of a pool service professional and/or an electrician.

Poor Water Drainage

If your pool has a tendency to flood in some areas of the pool deck, and if that runoff heads toward the pool, it needs to be fixed. Pool decks should slope 1/4″ down for every foot away from the pool. This helps ensure storm runoff heads to the lawn or surrounding landscape, not in the pool.

Look at the way water moves around the pool. If needed, rework the land to create natural swales to direct and slow rainwater runoff. You can also install drains and drain pipes, or install French drains in gravel around the pool deck. These drains should always be sloped to a downhill location, away from the pool and the pool equipment.


Heavy rains and storms are unpredictable and can be vicious. But with the right steps, you can protect your pool from any severe weather event on the horizon!

31 thoughts on “Heavy Rains & Swimming Pools

  1. Dollie Grenier

    I have a 18×33 above ground pool. We had tons of rain before we opened pool for the summer. Needless to say we had a lot of algae which we finally got the green out except for the walls which are stained green. Is there any way to remove this?

    • Hi Dollie, most vinyl liners do not stain from algae permanently. First balance the pH, alkalinity and calcium harness levels, and stabilizer. Shock pool with a triple dose, with a low pH level (7.2-ish) and brush the walls. An algaecide can be added after the chlorine level has come down to normal range. You can also try rubbing the walls from inside the pool, with a rough towel.

  2. Fran MUNSCHAUER

    We need innovation…We are about to get the heavy Barry storm that floods the entire back yard but pool is higher on a hill..And though we have only had the inground liner pool overflow 2X in 20 years,the amount of rain is warning worrying me. Unrealistically acc to my hubby, I suggested building a “berm” to surround the pool, since water rise has only been only a few inches above pool. He said that it would kill him to fill so many sand bags. Why hasn’t someone invented an inflatable tube like thing that could be filled with something that wraps around pool? When still covered this winter, storm rain caused the weight of rain on the cover to pull liner down. I suggested (if there are longer woods similar to 2X4’s,placing them across width of pool under cover might prevent weight of water from pushing cover down.Apparently having more pumps to pump water to street wasn’t a good idea either=too much water. I thought surely someone would have a unique idea to prevent water from entering pool. Any ideas????

  3. Felisa Canfield

    I have discovered that water from the yard is making it’s way under the concrete deck that surrounds the pool and draining into the pool between the deck and the top of the pool tile. Is this to be expected or is this possibly a construction error? Pool is 1.5 years old,

    • Hello, I guess you have a cantilever pool deck? One where the deck goes right up and over the pool wall, no separate coping stones around the pool edge, which would/should prevent what you describe. I would say that it is not normal, and is very troubling. A construction and/or engineering error. To have water washing under the deck will erode the soils eventually, and the water will over saturate the area, leading to deck heave during frost, and possibly damage to the pool deck and even the pool eventually. I would press them for a fast fix, or you may need to hire a lawyer – I think it is important to have fixed. It’s not your fault, so I would ask the builder, politely at first, to fix the situation properly, with permits, so as to have the county/city inspectors sign off on the solution and implementation, or other third party certification.

  4. Will alot of rain caused alot of wrinkles in the bottom of my above ground pool liner. It is not even 2 years old and has been very well took care of

    • Hi Joy, not usually, but if rain water is moving under the pool, or if water is trapped under the liner, because the water table rises, and the water has no place else to run to easily, it can ‘float’ the liner, or raise the liner (from water beneath the liner), and when the water recedes, the liner can reset with wrinkles. Other cause could be the (overlap) liner slipping down the wall, and wrinkles spreading across the floor, from broken coping strips usually. Good Luck!

  5. Thanks for pointing out how a submerged pump motor will likely need a replacement. My mother’s area got flooded pretty badly by the last typhoon. Her motor got affected heavily so I will be sure to advise her to get a new pump from In The Swim and install it herself

  6. Charlotte

    We have a Fox 16 x 32 vinyl inground pool. We will be on vacation for 5 days of which is forecasted for heavy rain while we are away. We have no one to monitor the pool water level for getting too high and over flowing, exceeding the height for proper swimmer function and getting water behind the liner at the coping.

    Are there any suggestions or devices to address these issues?

    • Hi Charlotte, One thing that could be done is to use an automatic pool cover pump, placed on a few boards to be elevated off of the top step, or tied to a ladder rail, or something to keep it at a very specific height, mid-skimmer. Automatic submersible pumps like the Water Wizard or the Ocean Blue 350 will turn themselves on/off, to maintain a certain water level.

  7. I had one landscaper out, and he refused to just reslope the ground, unless he could put in a french drain. But, if there is room to slope toward a swale from that right hand side of screen enclosure, why not just slope it away again, and why would I need this drain? I realize if you have no where to slope to, then a french drain is your only option. But, in my case, on all 3 sides, I can slope downward and away. I feel like a new river rock border on the newly compacted and sloped dirt, will do better perhaps to keep the water moving away too, then, just the mulch. I know swimming pool screen enclosures don’t have gutters on them. So, only resloping and/or french drain, but, again, if there is somewhere to slope it to, why not do that and not put in a french Drain? Now, it is true that the sloped dirt border is more horizonal then vertical, but, if it goes away, slopes away, that is the key right, not how steep the slope is? Right now there are flat areas on that side of screen enclosure, so water remains there till it stops raining and then goes away fairly fast, once the rain is done. I just don’t like the water laking up there while it is torrential rains, when I could divert it by resloping through a landscaper.

    • Davy Merino

      Hi Dana, I’m agreed on your points, and I can’t see a reason to use french drains if you have a steep enough grade, enough room to work and a short distance to meet swale or drain. However, if you have a small grade, and you dig a sloped (pitched) trench, perhaps dropping 1″ for every foot, and you fill with 3-4 inches of gravel, the method should work for most moderate storms. Over time the spaces between gravel will get filled up, and it eventually will stop working so well, however. Then the puddles start to form as it fills with water and oozes onto the deck (yuck). If you used grass or flat stone, or bricks, or even large river stones you would get faster dispersal of water than with gravel, which soaks up the water and reduces flow.

      • Hi Davy,
        Going on the premise, that I don’t need a french drain, or want one, if I can re-grade correctly. What is considered a steep enough grade? I have enough room to work and the swale is 10+ feet away down a slope. SO, in 1 foot, how much slope to be considered steep enough please? I need to run this by a landscaper who can re-grade too. THe key is I don’t want to lose my newly formed border, and trying to keep water from going under the patio, with this new border sir. Right now, after 23 years, I lost my original compacted dirt border, I put mulch on for years and the patio now is as high as the grass edging 1-2 feet away. Over time, I think the border was eroded and the grass got higher. St. Augustine I believe can do that.

        • Davy Merino

          Hi Dana, as a minimum, a 5% slope may be normal, but 10% may give more room for error. I think a slope of 1″ per foot would be a good bet, or about a foot drop within the 10 ft distance to the swale.

  8. Hi Davy,
    I guess my 23 year old sloped compacted dirt border is now flat and thus the grass and the patio are the same height. So again, when it rains, the water lakes up in places on that right hand side. Now, there is plenty of room to slope downward, mainly horizontal slope, so, should the border be a newly compacted dirt border with mulch on it or a newly compacted dirt border with rock on it? I don’t want to lose the new slope anytime soon. I just think I lost the slope to erosion over time, 23 years and just noticed last summer during torrential rains, the water laking up and the red mulch swimming there some, so, I figured best to re-grade downward, to the swale there on the right hand side. I think the water came from the heavens or off the screen enclosure onto flat land there, and thus if I could hire a landscaper to regrade, how can I do it not to lose it anytime soon?
    Is a newly compacted dirt border, with felt, or some sort of gravel/sod compacted, then, rock on top the best, of course it goes toward the newly compacted new sod slope too. The border is what I am trying to protect from disappearing anytime soon. The space is NOT tight, it just got flat, it has something to drain down to. I mean I think it worked good for years, but, over time, erosion I think took over and flattened that border area between the swimming pool patio and the edging of grass.
    Please give me your best answer, the sloped compacted dirt border with rock on it, wouldn’t that make the water go down and sink in near the swimming pool patio? 1 landscaper, which I think he is wrong, drew this box next to the patio with gravel in it, but, that again, doesn’t have the rock on a sloped compacted dirt border, which I think is better. I am not trying to install a french drain, just draining the water or sloping the water away with the best border I can find. Please give me your opinion please on what type of border.

    • Davy Merino

      Hi Dana, the most important thing is the slope, you can top it with anything – rock, mulch, grasses. I’m sure the landscaper would slope it for you, to prevent standing water in heavy rains, it should be drained towards the swale, yes. Landscape fabric can be placed under the rock, on top of compacted or tamped soils, and covered in decorative rocks and stones. that will prevent most water from draining under the pool.

  9. for Problem #5, poor water drainage, your suggestion if you can do it is to rework the land to create natural swales. Since on say the right hand side of screen enclosure, I can slope downward, then, I should re-grade by a landscaper the land to slope downward and perhaps create a 1-2 foot rock border on this compacted sloped border to go down to Grass, so that water drains away from the side of my swimming pool screen enclosure instead of laking up there which it does now. If I can actually slope away, Or as you call it, create a swale away on all 3 sides, then, I see no reason to put in any french drains. I don’t exactly know why the ground got higher around the right and left hand side of screen enclosure, it used to be a compacted dirt border, over the years, 15 to be exacty, I kept putting mulch in this border, but, now, the ground is not sloping as well as it did when I moved in 15 years ago. I assume, that a landscaper can re-grade this area on all 3 sides and put some sort of rock border sloped away to the sloped grass too and the water won’t any longer lake up next to the screen enclosure on the left hand side. If the water after a rain stays there, like it does now, it is because the ground is not properly sloped away, but, can’t the re-grading be done and perhaps put some sort of compacted gravel/sod backfill in before putting that 1-2 foot border and sloped to grass, and/or some erosion mat(felt), what sir is the best way to re-grad this properly?

    • Davy Merino

      Hi Dana, you are on the right track yes, dig it out and regrade the area to slope away from the pool, or when space is tight (under 2-3 ft) French drains can be used, or for especially high volumes of water

  10. Phyllis Bird

    I’m preparing for hurricane Irma should I drain some water out of the pool to insure that the pool will not not run over onto the lanai. The drain on the lanai which runs the length of the lanai cannot handle the amount of rain we will get; therefore it will overflow into the house. Will this damage the pool in any way
    I’m talking about a foot.

    • Davy Merino

      Hi phyllis, if you have a separate main drain and skimmer valve, you can still operate the pump – with the water about a foot low. If the ground becomes super saturated, hydrostatic pressure can lift a pool out of the ground, so I wouldn’t drain more than a foot of water, at a time – you can do it repeatedly, during the rains – using the filter pump, submersible pump or a siphon set-up with the vac hose or garden hose.

  11. just experienced flooding with Hurricane Harvey. My pool guy tells me i have to remove my jacuzzi heater because it can explode and blow up my house. my home flooded, now we are in restoration mode no longer under water. i have disconnected equipment prior to storm.

    • Davy Merino

      Hi Armando, to prep for flooding, I would probably remove the entire spa pack from the spa if possible, if it was in danger of standing in water over 3″ deep. If your heater is electric, it will not explode, only gas heaters do that – but not very often, not from flooding, I don’t believe. Gas heaters should have the gas shut off however to prevent possible damage to the gas line from heavy erosion or hill creep during flooding.

  12. Hello, I have an above ground fountain with no plumbing holds about 3500gal. Can I simply run the hoses over the top of the fountain. Algae is beginning to build and settle. The wall is 2ft high and the water level sits around 18in. I’m out of options. Everyone says it won’t work but with a strong enough pump won’t it it be able to filter even with the slight incline.

    • Hi Adam, absolutely you could run rigid PVC pipe, or Flex PVC pipe over the wall of the fountain to circulate the water with a pump. Attach a filter to it, and use a chlorine tablet floater and you’re all set! Use 1.5″ PVC, with 90 degree elbows to go up and over the wall, and another elbow on the pipe end, underwater. Place the suction pipe on the floor, but elevate the return pipe to discharge 4-5 inches above the floor, and point the 90 elbow toward the wall, to develop a circular flow pattern around the fountain. You should use a Hayward safety grate on the suction line to reduce entrapment hazard, or place a large strainer basket or strainer box around the suction pipe, for safety and to strain out the leaves and debris. You could also attach a lily pad skimmer or floating skimmer to the suction line. On the return line you can use an eyeball fitting to create more return pressure if needed. You can use a small pump and filter system for aboveground pools, a small sand filter can also be used, with a plug in type pump, like the Hayward VL, Sand Master or Intex Sand filter – https://www.intheswim.com/c/above-ground-filters?pcode=208&scode=SOCIBLOG .

      Now if you wanted to, you could do the same thing as above, except use a large rotary drill or core drill to cut two holes in the lower wall of the fountain, run the pipes through the wall, and then patch with hydraulic cement and plaster to waterproof the pipe on both sides of the wall. then you can run the pipes underground – if that matters! Over the wall will work great, I’ve done it before, no problem.

  13. Hello,

    When draining your pool of excess water where is it supposed to go? My neighbor is dumping chlorinated water into our neighborhood storm drain which goes straight to the Bay.

    • Hi Kelsey, most cities/counties around the Chesapeake Bay have ordinances that state that water must be de-chlorinated before release into the storm drain. in practice however, excess water or filter backwash water will likely have some chlorine in it, at least as much as found in tap water (Fairfax county water often has more chlorine in it than the average pool). The option to draining to the storm drain is to drain it to the woods or a lawn that can absorb the water, without erosion concerns. Most pool water is not full of dangerous chemicals, and is even potable or could be used as drinking water (in an emergency). Chlorine, clarifiers and algaecides are not a large problem for the bay. Phosphates, nitrates, industrial and farming pollutants are the real enemy to aquatic life, pools or pool water (in most cases) is not harmful to the bay.

  14. We have been getting some heavy rains and I have a high alkalinity with the rest of the chemical readings as good. Would it make sense to let the pool overflow for a little while. There was someone who said that the chemical that makes alkalinity high stays at the top of the water. So flooding the pool during a rain would lower the alkalinity. Is this correct?

    • Rain water is typically low alkaline and low pH, so it is possible that heavy rains, or several inches of rain can have some small effect in lowering Alkalinity, but maybe not as much as you need. Alkalinity should be in the 80-120 ppm range, and can be lowered by pooling acid in a calm area of the pool. It also lowers pH, so you often have to then raise the pH, which raises alkalinity, and so on, until you get the alkalinity in range. Or you can lower the water in the pool, and refill with fresh water of a lower known alkalinity level.

  15. It’s interesting that contaminants in the pool can be a big problem for people who get a lot of rain and runoff. It makes sense that this could be problematic because it would make the pumps and cleaning system work harder. It’s something I’ll have to remember to make sure I can get the pool pump repaired before a lot of runoff gets into the pool and makes it dirty.

  16. These are all good things to look for when experiencing a murky pool. In many cases a pool could handle a good bit of rain, and should not overflow, and as you mentioned the pitch of the concrete decking must run water away from the pool coping. All of these items would not be a concern to a pool owner with a quality built pool, but not all pools were created equally either!

  17. […] means you should run the filter pump longer. Rain washes in lots of pollutants, dust and oils, and heavy storms wash off of nearby trees or flow into the pool from nearby planters. This brings in phosphates, […]

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