Heavy Rains & Swimming Pools

rainy-poolMother nature has certainly been giving us some strange weather lately. In California, we’ve been pelted by torrential storms, with several inches of rain in a few hours.

Our call center has taken hundreds of calls from distressed homeowners, desperately seeking solutions to heavy rains and flooding, or fixes for pool problems created by heavy rains.

Californians – Take these steps to protect your pool, or clean-up after heavy rains.

Problem #1 – Too much Water in the Pool

Lower the water level in your pool to keep proper skimming action, and to avoid contamination from planters and deck area flooding.

For most pools with a sand or DE filter, the simplest way to lower the water level is to place the multiport valve onto 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.

lil-giant-water-wizard-cover-pumpSome pools have a hose spigot plumbed after the pump, or on the filter valve, which you can connect a garden hose, to lower water level. Or, you can use a submersible pump, aka 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, and attach a vac head or use a heavy item to hold the hose on the first or second step, the pool ladder, or swim out.

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! Keep an eye on it though!

Problem #2 – Contaminants in the Pool!

From Run-Off: When a backyard pool gets 5 inches of rain in a few hours, flooding can result. If surrounding planters or 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.

flooded-pools in Califonria, image by istockphotoIn 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 brush, and near continuous filtering. Clarifiers and flocculents can be used to speed up the process considerably, and may be needed for sand filters.

As the water clears, use a phosphate remover chemical like Phos-Free or Sea-Klear to naturally consume phosphates in your pool. Just pour it into balanced pool water, run the filter for 24 hours, then backwash.

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


Rain can also destroy your pool’s water balance. It dilutes the cyanuric acid, and can also soften the water, lowering calcium hardness, and it can affect pH and alkalinity as well. Acid Rain falling through smoggy summer air hits your pool at a very low pH, reducing pool pH and alkalinity. Be sure to test your water with a complete test kit like the K-2005, or use 7-way test strips.

Problem #3 – High Wind, Debris & Projectiles

Before a storm hits: Store all loose toys, furniture and cleaning equipment that could become airborne in high winds. Don’t cover the pool, which can be damaged severely in a heavy storm.

After a storm hits: Clean the pool, lower the water level, check the water balance and the chlorine level, adding sanitizer if needed. If your pool is a funky color, super-chlorinate with some pool shock, and run the filter overnight. It’s best to remove leaves and debris from the pool, and lower the pH to 7.2, before shocking the pool.

Problem #4 – Flooded Pool Equipment

Keep the filter running, however if flood waters threaten to submerge the pool pump, shut off power to the pool on the main home panel. If you can safely remove the pump, store it indoors, if the pump motor becomes submerged, it will likely need to be replaced.

Regular rain falling on your pool equipment will not usually cause any harm, even if it lasts for days on end. If concerned however, you can build a lean-to of some sort over your filter pump. Flooding however is the real problem. Sand bagging your pool equipment could save you from pump replacement, if flood waters rise above the equipment pad.

Problem #5 – Poor Water Drainage

If your pool has a tendency to flood in some areas of the pool deck, and if run-off from heavy rains ends up in the pool – it needs to be fixed. Pool decks should slope 1/4″ for every foot, and storm run-off needs to go somewhere; never in the pool.

Look at the way water moves around the pool, and rework the land to create natural swales, or install drains and drain pipes, or install French drains in gravel around the pool deck, sloped to a downhill, away from the pool location, and also away from the pool equipment.

Don’t let heavy rains and storms make your summer a bummer, follow these tips to avoid these 5 pool problems caused by heavy rains and summer storms!

Davy Merino
InTheSwim Blog Editor



Heavy Rains & Swimming Pools — 21 Comments

  1. 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.

    • 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.

        • 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.

  2. 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.

    • 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.

  3. 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?

    • 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

  4. 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.

    • 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.

  5. 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.

    • 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.

  6. 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 – http://www.intheswim.com/c/above-ground-filters .

      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.

  7. 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.

  8. 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.

  9. 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.

  10. 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!

  11. Pingback: How Long to Run Pool Pump? | InTheSwim Pool Blog

Leave a Reply

Your email address will not be published. Required fields are marked *