Draining hot tub into a pool/refilling from pool

[mjc123]

I was recently reading about others draining their hot tub/spa into their pool, and also the reverse: refilling it from pool water (though it wasn’t the same person).

Wondering about the pros and cons. The pro is definitely saving water. But in my mind, if the water in the hot tub is “dirty” enough to require draining, then would I not be potentially “dirtying” the pool water as well? I realize the volume is very different (1500 litres vs 70k) but over time wouldn’t I be building up the levels of “undesirable contaminants” in the pool?

Interested in people’s thoughts

 

[PoolGate]

Are these two totally separate bodies of water? If so I've never heard of anyone doing this.

 

[mjc123]

Are these two totally separate bodies of water? If so I've never heard of anyone doing this.

There’s a few threads on here about it. One example:

Can I drain my Chlorine Hot Tub into my Chlorine Pool?

Hi All, I have a roughly 30k-35k gallon pool with chlorine and a 500 gallon hot tub. I typically dump hot tub water quarterly out into the lawn, but I wondered today if it was safe to just dump it into the pool instead, and then just test/rebalance the pool water if required. If it's common...

www.troublefreepool.com

There are others on TFP, and many others elsewhere on the internet.

I’m not sure it makes sense for me anyway if I plan to do an Ahhsome purge on each draining cycle, but perhaps in cases where I don’t

 

[phonedave]

In theory, if the hot tub is not disgusting, then the pool should be able to handle the miniscule amount of contaminants. When I change my water in my hot tub, it is not because it is horribly dirty, but because I am being proactive. But it is only 300 gallons for me. In the grand scheme of things, it is not that much. I also cannot refill my tub from my pool, since my pool is salt and my tub is not.

Also, as you said, I Ahhsome purge before draining my tub, and I would not want that in the pool

 

[TopJimmy]

When I was setting up my separate pool and spa for the first time, the pool water was testing good but the spa was all over the place with the various levels. I pumped my spa water into the pool, mostly, then pumped it back and all was well with both. Haven't done it since then, but when (or if) I winterize my spa, I was planning to do the same (to below the spa jets) so I can easily blow out/plug the 9 jets.

 

[PoolGate]

You are only talking about 1500 liters (400 gallons). How much is your water? Is this just a financial issue? For me this would not even make a $4 difference on my bill as I pay 1 cent per gallon. I would drain it into my backyard.

 

[A.O.]

So I always fill my spa with pool water, the reason being that I have a LOT of iron in my water and the sand filter in my pool works wonders at eliminating it. If I just fill the tub with the hose it turns into a mess. This I have learned over the years here by trial and error. I do not drain my tub into my pool, but I may give it a try sometime. Both are salt systems.

 

[Newdude]

then the pool should be able to handle the miniscule amount of contaminants.

+1. In theory it's one or two people's residuals dispersed in 10k gallons like they were swimming. They'd make more residuals in the 104 degree hot tub and all, but not enough to change the price of beer.

The only reason the hot tub water is gross is because how concentrated it is with so little gallons per bather.

But with clean fill water (when applicable), I wouldn't blink to dump it and fill with the hose.

 

[phonedave]

So I always fill my spa with pool water, the reason being that I have a LOT of iron in my water and the sand filter in my pool works wonders at eliminating it. If I just fill the tub with the hose it turns into a mess. This I have learned over the years here by trial and error. I do not drain my tub into my pool, but I may give it a try sometime. Both are salt systems.

I can see this. It would help me as well, not with iron, but with pH/TA. But since my pool is salt and my hot tub is not, it's not an option. Well it is an option, some people like salt water just for being salty.

 

[PoolGate]

I can see this. It would help me as well, not with iron, but with pH/TA. But since my pool is salt and my hot tub is not, it's not an option. Well it is an option, some people like salt water just for being salty.

The little bit of salt in your pool (3 parts per 1000) will be barely noticeable in the hot tub. Most cannot even taste it in the water. Reference the ocean at 35ppt.

 

[A.O.]

I can see this. It would help me as well, not with iron, but with pH/TA. But since my pool is salt and my hot tub is not, it's not an option. Well it is an option, some people like salt water just for being salty.

Have you ever thought about going to salt in the hot tub? I did about a year ago with the Saltron Mini chlorine generator and wish I had done it a long time ago. And I had salt water in my hot tub a long time before going with the Saltron due to filling it from my pool!

 

[SJPoe]

I don't drain the hot tub to the pool, but the last couple of times I have filled the hot tub from the pool.

When draining the hot tub, I typically do an AhhSome purge first, so I'm not sure putting that into the pool is a good thing...why dump dirty water in my nice clean pool ? I have a nice handy drain that heads to the storm drain, so that's what gets used.

For filling, the last couple of times I have filled from the pool. 450 gallons barely makes a dent in the pool volume, plus it is clean, clear, pretty much balanced and ready to go. It's usually at 80+ degrees which saves a little heating time (I'm not worried about the cost, but 30F is extra hours of heating time that my wife is without her hot-tub...happy wife...happy life).

As we're on a well, I would generally pre-stage about 250 gallons over a day or so (on the deck above the tub) so that when I was ready to fill, the first 50% was already done, and I just had to top up. It would still take a few hours to fill - you can't just blast 5 gallons a minute from your well for hours on end...and then that water is at 50F so would take a while to heat...

The only real downside is the CYA level - the pool is 60-70, and usually I'd run the hot tub at 30, so you have to run chlorine a little hotter, but as it's just the wife and I anyway, its not like we're trying to sanitize for 25 strangers or something. If she's got it, I've probably got it already too. I generally check the chlorine level in the hot tub every morning and add LC as required, and usually add a little after every use. Maintaining 5-10 FC rather than 3-7 isn't really a big deal either way.

Our pool is now salt, and to be honest, it feels better in the pool, and in the hot tub. I haven't noticed any issues. The spa manufacturer offer an SWG generator option (not sure if its a retrofit option tho), and Chlorine is going to break down into Salt anyway...so I fail to see a reason to worry.

 

[Newdude]

why dump dirty water in my nice clean pool ?

Now that you mention it....... when that half gallon of stagnant water on my solar cover rolled off at the end each time, it made me want to cry. The pool absorbed it in mere seconds, but I don't believe I'd be able to stomach watching it happen for as long at it took to drain the spa.

I stand by my comment that the pool could handle it. But I couldn't.

 

[SJPoe]

Now that you mention it....... when that half gallon of stagnant water on my solar cover rolled off at the end each time, it made me want to cry.

I know... that is the worst....lol

 

[phonedave]

The little bit of salt in your pool (3 parts per 1000) will be barely noticeable in the hot tub. Most cannot even taste it in the water. Reference the ocean at 35ppt.

The concentration in my pool (3200 - 3400 ppm) would be the same concentration in my tub - which is noticeable (I CAN taste it).

It is not a matter of noticing it or not, it is a matter of having that concentration (and eventually higher, since I use liquid chlorine) going though my heater, when I don't have any reason for that salt to be in there in the first place. If I was using a SWCG in the hot tub, then it is a different story - having salt vs. the benefits of having a SWCG.

 

[phonedave]

Have you ever thought about going to salt in the hot tub? I did about a year ago with the Saltron Mini chlorine generator and wish I had done it a long time ago. And I had salt water in my hot tub a long time before going with the Saltron due to filling it from my pool!

If I could find a SWCG that I liked, I think I would. I am not a fan of the drape over. I am also not a fan of having an extension cord running across my patio. I guess I could do the electrical work to put a receptacle in a good place. Maybe next spring (I have to do some electrical work on my pool as well, since I moved my skimmer and return location) so maybe I'll do all of that at once. I guess I will eventually bite the bullet and use a SWCG in my hot tub too (but I would really like a built in one - but that is just me)

 

[PoolGate]

The concentration in my pool (3200 - 3400 ppm) would be the same concentration in my tub - which is noticeable (I CAN taste it).

It is not a matter of noticing it or not, it is a matter of having that concentration (and eventually higher, since I use liquid chlorine) going though my heater, when I don't have any reason for that salt to be in there in the first place. If I was using a SWCG in the hot tub, then it is a different story - having salt vs. the benefits of having a SWCG.

The salt level in pools will not hurt any of your equipment. Most people like the softer feel of a little salt. Even if my pool wasn't a "saltwater" pool per se, I would still add salt to it.

 

[mjc123]

You are only talking about 1500 liters (400 gallons). How much is your water? Is this just a financial issue? For me this would not even make a $4 difference on my bill as I pay 1 cent per gallon. I would drain it into my backyard.

Mine's about the same:
$1.128 / m^3 + $2.259 / m^3 for what they call "wastewater discharge" (i.e. sewer maintenance, I guess)
so $3.387 / m^3 total
1 m^3 = 264.172 US Gal, so
$0.0128 / US Gal

Plus the various base fees, but those aren't variable.

In any case, no, it's not really about the cost at all, more about just not liking to waste water if there's alternatives. To be clear, I have only ever drained it into my backyard. But I was curious about whether there was any value in not. Honestly, using the hot water to warm the pool slightly would probably save me more $ than the cost of the water itself, lol. Electricity is not cheap here

 

[PoolGate]

Mine's about the same:
$1.128 / m^3 + $2.259 / m^3 for what they call "wastewater discharge" (i.e. sewer maintenance, I guess)
so $3.387 / m^3 total
1 m^3 = 264.172 US Gal, so
$0.0128 / US Gal

Plus the various base fees, but those aren't variable.

In any case, no, it's not really about the cost at all, more about just not liking to waste water if there's alternatives. To be clear, I have only ever drained it into my backyard. But I was curious about whether there was any value in not. Honestly, using the hot water to warm the pool slightly would probably save me more $ than the cost of the water itself, lol. Electricity is not cheap here

Not sure you can "waste" water, per se. It all goes back down into the ground.

 

[Mdragger88]

If I could find a SWCG that I liked, I think I would. I am not a fan of the drape over. I am also not a fan of having an extension cord running across my patio. I guess I could do the electrical work to put a receptacle in a good place. Maybe next spring (I have to do some electrical work on my pool as well, since I moved my skimmer and return location) so maybe I'll do all of that at once. I guess I will eventually bite the bullet and use a SWCG in my hot tub too (but I would really like a built in one - but that is just me)

When you get to that point if there’s not one that’s designed specifically for your tub the controlomatic ones have an in line option/kit.