Help me overcome my fear of shallow water tables
July 28, 2022 4:52 PM   Subscribe

The city I’m in sits on 3 feet of topsoil on top of a mile thick limestone pancake (a karst landscape). I’m thinking of adding a pool and filling it with groundwater. I already use well water for landscaping but I’m not ready to swim in it yet.

For filling a pool the choice is a shallow well or a water tanker (city water can’t be used), and virtually everyone does the former. The problem is this: the city has no sewage system. There’s probably about 100,000 septic tanks all in close proximity and roughly 50 in the square mile around my house: 50 sixty year old buried septic tanks. Those things have got to be leaking. There don’t seem to be health problems linked back to this but I’m squicked out. Water tankers are an expensive and awkward option. Can you help me feel okay about a shallow well?
posted by Tell Me No Lies to Home & Garden (8 answers total)
IMO you are correct to be worried. Septic tanks are built to leak- ie they have leach fields that expend effluent water into the water table - bacteria eats the solids. They are basically terrible. I'd not want to drink water from around them. Swim in a river or lake nearby?Well we all take risks, but those are quite a bit bigger so the parts per million of effluents is hopefully less (knock on wood). A pool? No thanks.
posted by The_Vegetables at 5:17 PM on July 28, 2022 [1 favorite]

I don't think this is about feelings at all, it's about science. Have the water tested and see if it's safe. Maybe you'll want to do this yearly.
posted by fritley at 5:23 PM on July 28, 2022 [13 favorites]

What fritley said.
The cautious plan is to dig a test well and monitor it with regular tests from the extension service or private lab. Also maybe one-time analyses from samples around the property, bc subsurface flow is not always obvious.

It could be totally fine! Maybe even highly likely. It will be good to know the evidence-based answer for your specific situation.
posted by SaltySalticid at 5:35 PM on July 28, 2022 [1 favorite]

Presumably the pool is lined so that groundwater isn't always leeching in? Assuming there's very little exchange of water between what's in the pool and what's outside the pool, everything inside the pool will be treated with chemicals and the water will be sanitized as part of basic pool maintenance.

Even if you initially fill it with water from a shallow well, all the nasty stuff in that water will soon be treated, neutralized, and filtered out. The important thing is to add the proper balance of chemicals and keep testing the water.
posted by RonButNotStupid at 5:41 PM on July 28, 2022 [8 favorites]

Best answer: You will be treating your swimming pool water with standard swimming pool chemicals, yes?

Consider public swimming pools: those pools are a soup of random people's butts. Pool rules typically require showering (i.e., washing one's butt) before one enters the pool, but how many users actually do that? And yet, the chemicals make it safe. I spent many a summer swimming in public pools during my youth and was always fine (along with the majority of the population of my town) because the pool water was properly treated.

The groundwater you'll use to fill your pool will have been extensively filtered and aged as it seeps through the limestone before reaching your well. Limestone is an excellent filter.
posted by heatherlogan at 6:16 PM on July 28, 2022 [4 favorites]

Best answer: FWIW we filled our pool with literal ditch water. As in, divert the ditch into the pool, fill it, divert it back to the ditch.

The people who regularly filled pools said interestingly, the pool full of ditch water didn't look far different than the pool filled straight from the city's water supply.

More to your point, though, what you would do at that point was turn on the pool filtering system, use shock treatments of pool chemicals etc for a few days, and within several days it was pristine pool water. (And again, the "pool people" didn't seem to feel this was too far off from what you would have to do if you filled with regular city water."

Also, our pool was the type that it was impossible to drain (the walls would collapse). So it would sit all winter, filled with water and covered.

When we re-opened the pool the next spring, the water quality was FAR FAR worse than what we had seen filling it with literal ditch water.

Didn't matter. You skim off dead bugs, whatever, start running the pool filter, hit it with those pool chemicals per the instructions for several days and at the end of that, the water is crystal clear, pristine, meets all tests, etc.

Point is, the cleanliness and safety if your pool water is determined by the filtration system and chemicals used to keep it safe and clean, not so much the water source.

If you keep on top of it with recommended filtration & chemicals, it will soon be safe no matter where the water came from. If you DON'T do that (or stop for any reason, such as end of season) it will soon become very dirty and unsafe - regardless of where the water came from.

That goes particularly for organic type contamination, such as you would see from septic tanks. If you say a chemical production plant that was leaching chemicals into the local water supply, then I don't know that the regular pool filtration and chemicals would do much about that (but then - does your city water supply's do any better? It might only if they are testing for those specific chemicals and taking necessary steps to reduce or eliminate them when they do. Regardless, that type of thing and not normal organic sources, are the real potential problem here.)

Regardless, in rough terms, as far as establishing an initial water supply for your pool, all three of these are going to be approximately equivalent in terms of how "gross" it is and also how "safe" it is:

- City water supply
- Tank truck
- From a nearby well

ALL of those are going to require your pool filtration system and chemicals to make them and keep them safe enough to swim in.
posted by flug at 6:54 PM on July 28, 2022 [5 favorites]

If you’ve ever sat in a hotel hot tub - or as I call them, a crotch broth - you’ve been saved by the marvels of chlorine. As long as you test the pool and nuke it with pool chemicals I can’t see how it could be worse than a hotel hot tub.

And yeah, my friend filled her little swimming pool from the city water in a city known for having good tap water, and within a week of not chlorinating it properly it was a cesspool, even though it started with world-famous good tap water.
posted by nouvelle-personne at 7:17 PM on July 28, 2022 [1 favorite]

I don't have a pool and never will, but somehow I ended up on pool cleaner TikTok and what they can do to an absolutely irredeemable-looking pool should set your mind at ease. Maybe search some of those videos out if it would make you feel better!
posted by misskaz at 5:22 AM on July 29, 2022

« Older Alternative to InDesign for a Basic Print Book   |   Drive by Dragging (my custom route on google maps) Newer »

You are not logged in, either login or create an account to post comments