Would this body of water stay clear without chemical?

[mehrzad]

I have a unique situation. I live on a hillside property with a Well water & 100 new trees. Last year I experienced pump failure which made me realize I need a backup plan for irrigation that is not dependent on my well water & electricity. So I like to build a 9000 gallon pool 35'x7'x 5'deep in my backyard which is 20' above the orchard. I will use about 1000-1500 gallon of water a week & I like to gravity feed the water for the irrigation from this pool & replace with fresh water. We did not intend to have a swimming pool, but it sure will be nice to jump in once in awhile (considering we live in AZ).

Obviously I cannot use chemical in the water, but I can circulate, aerate, other means of cleaning & even go as far as running the water over some water plants for some purification. I can even drain it completely and start over if necessary.

I would love to hear some experts opinion & feedback as:
1) would using 10% of water per week imitates a running water?
2) would draining it off and on hurt the shotcrete? what if I do not plaster the pool?
3) any other method I can add to keep the water clear.

thank you all in advance.

 

[JoyfulNoise]

If you're asking about running a "natural swimming pool" (NSP), we do not advocate those types of pools on this forum. They are, to put it simply, dangerous at best to swim in. A pool like the one you are describing would never stay sanitary. Clear water is not the goal, sanitary and clean water is.

You have to use a method of sanitation to keep a pool clean. Chlorine is really the only proven method of keeping a pool sanitary and clean. Also, in that scenario, you would be constantly causing a 10% change in chemistry levels every time you decide to irrigate. That will require you to add more chemicals to the water, not fewer because your pH will swing wildly and your sanitizer levels will change.

However, chlorine is not detrimental to most vegetation. It would be effectively neutralized within the first 3" to 6" of soil as it reacts with organics. Since the volume of water is so small compared to the surface area of irrigation, I doubt chlorinated water would have any impact at all. The pH of pool water is typically in the mid-7 range which is MUCH, MUCH better than the irrigation water you would typically use here in Arizona (8.0+). If you did not want to directly irrigate with pool water, you could add a 1,200 gallon surge tank to your setup (or build a concrete retention pond) where you could discharge the pool water to and then let the chlorine levels come down naturally. After the chlorine levels fall, you could then discharge the water from the pond into your irrigation furrows.

So as long as you don't mind spending LOTS of money on chemicals to constantly replace what you lose to irrigation, you could use the pool in the manner you speak of. You do not want to constantly expose plaster to dry air, so you would have to perhaps tile the pool or at least add something like three rows of 6" pool tile to the water line so that the plaster below is not exposed to heat and dry air. Since it's a small pool, you could spend lots of money on it and tile the whole thing which would avoid plaster issues....

 

[mehrzad]

Thanks Matt. The intent was not building a NSP or swimming hole, but a reservoir for irrigation without full expense of pool equipment & its maintenance. Of course I don't want to have an unsanitary body of water in my backyard. Perhaps cutting down the volume may help. But if not possible I may have to build a regular pool. thanks

 

[JoyfulNoise]

Well, just to give you some numbers to toy around with - an unsanitized stagnant body of water can be exposed to algae and bacteria. Algae populations will double in size roughly every 4-6 hours (limited by sunlight mostly) and bacteria colonies double in roughly 45-60 minutes. So, once you fill the "tank" you've got about a single use of the water before it becomes unsanitary...kind of like a bathtub.

 

[AimeeH]

I agree with joyfulnoise/Matt here. Unless you've seen a gross pool, it's hard to imagine. We had a two acre pond ( until the 10/5/2015 flood took out our dam) that would have been better to swim in than a non circulated pool as it was spring/steam fed. I think you'd be much better off with large agricultural closed irrigation tanks and a pool of your own.

As Matt said a stagnat body of water become dangerous with algae etc, but is also a mosquito breeding ground. Whereas a natural pond is not so much a mosquito breeding ground because there are fish that like to eat the larvae.