The Woodstock thread branched off into water supply and treatment (these things happen!) so I’ve started this thread.
Mods- please feel free to merge those replies here.
I treat my water with Scotch. Or is it my Scotch I treat with water? 
(Blended Scotch of course. Proper single-malts I enjoy neat…)
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Ha! Bourbon here
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You put water in Bourbon? Weird.
(Whisky dilution thread coming in 3… 2… 1…)
I put frozen water in bourbon sometimes.
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I fear we’re hijacking this thread. I haven’t read the Woodstock thread, but I’m pretty sure booze isn’t what the OP intended to discuss. Maybe we should take this to the Intoxicated Hangout…
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Here in the UK we source our drinking water from impounding reservoirs (water running off the catchment surrounding the reservoir), rivers and boreholes. Different sources need different amounts of treatment and that will dictate the treatment processes used. For example borehole water is relatively clean compared to upland sources which are high in dissolved organic content (often called ‘colour’) and river waters which are often ‘brackish’ and subject to large variations in quality.
The main treatment processes are screening (especially for river sources), flocculation, clarification, filtration and disinfection.
Starting with flocculation we add a coagulant such as ferric or aluminium sulphate, as well as coagulant aids such as lime slurry and a polyelectrolyte. That gets mixed with the raw water in a flash mixer before moving into a large tank called a flocculator. The DOC or colour is dissolved in the water and won’t settle out of its own accord. For the non chemists the coagulant promotes the forming of colloids. The water then goes from the chemical flash mixer into a flocculator which is a big tank with a slow moving mixer. As the colloids hit each other they form floc which grows in size aided by the lime slurry which gives the floc more mass and the polyelectrolye which acts a little bit like a glue.
The water then goes into large sedimentation tanks called clarifiers where the (comparably) heavy floc starts to sink or precipitate. That sinking is countered by the upward flow of water into the clarifier. The result is the formation of a literal ‘blanket’ of floc (which by this point is classed as sludge) somewhere in the middle of the depth of the tank. The blanket acts as a filter, allowing clean water to pass upwards through the blanket whilst collecting the floc/sludge. The sludge is bled off periodically and either sent to sewer or further treated such as in plate presses and turned into a ‘cake’. The whole clarification process works on the principles of gravity and upward flow. Managing blanket levels and flows through the clarifiers is a bit like spinning plates in the dark!
The water now appears to be clear in comparison to the raw water but that’s just the front end of the process. The next stage is filtration. Usually that takes the form of a rapid gravity filter. Imagine a deep chamber with upward pointing nozzles in the floor and with a second chamber below. The upper chamber is part filled with a media such as sand, anthracite or even granular activated carbon. The water enters the chamber from the top and filters through the media and out via the nozzles. As the media becomes blinded you get a differential pressure (headloss) between the top chamber and the bottom chamber (called a plenum chamber). There are also instruments which measure the turbidity of the filtered water and those instruments along with the pressure senders and a timer feed into a control system. When one of the three factors hits a trigger point the filter closes its inlet valves and basically reverses it’s flow. So now water and air is pumped up through the media via the nozzles at a controlled rate which has the effect of cleaning the media. This is called backwashing and the backwash water generally goes to sewer. This is why there are usually several RGF filters effectively in parallel so one can be backwashing while the others are in service. After the first stage filters the disinfectant is dosed along with some form of pH correction. The water then goes through a second set of of RGF’s which act as manganese contactors for the removal of manganese. The treatment process is basically now complete.
This is a simplified description to some extent; there are separate systems for making up and dosing chemicals as well as dual/triple validated instruments measuring al sorts of parameters.
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Are there significant differences between the treatment of drinking water and wastewater, besides the level of purity or cleanliness achieved?
Having potable drinking water piped to homes is a highlight of civilization. I am dumbfounded at how many people drink bottled water (usually from very similar sources as are feeding their taps) for no good reason other than marketing. (I buy 18l bottles in the place where I work, because the tap water is taken from a local river and inadequately treated, at least as far as flavour and mineral content is concerned.) I usually learn the phrase for “tap water” in the language of the countries I visit (not, of course, in places where the tap water needs to be boiled first). In Belgium this does not work. They will not give you a glass of tap water in a restaurant. I wouldn’t mind if they gave me 1.5l for a euro, but it’s 250ml for three euros…
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Wastewater treatment is quite similar in some ways to the flocculation/clarification stage. Their processes are called primary, secondary and tertiary. They use a coagulant to settle out heavier solids to form a sludge which is often digested on site with the methane collected and burned in CHP engines which generate electricity to be used on site or fed back into the grid.
Most treatment works use the activated sludge process pioneered here in Manchester in the labs at Davyhulme. I’ve never worked in wastewater treatment (in clean water circles it’s called ‘the dark side’
) but I’ve got a very basic understanding. If you do a search for the activated sludge process you’ll find more info.
Wastewater processes are being developed all the time to help meet ever more stringent standards and to reduce the footprint of treatment works Such as the Nerada process.
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“The dark side” I love it!
i grew up the day i got one of those office-style water coolers at home with the purified goods. now my cat and i have a nice gossip spot
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Very interesting, thank you for the explanation.
We have municipal water where we live, but there are two older wells on our property. When the house was built (1967), it wasn’t connected to the municipal water supply and the water was taken from the wells. Since it feels extremely luxurious to water our garden and stuff like that with potable high quality water from the tap, I recently bought a well pump to use for such purposes.
I’d like to have the well water analysed, just to know what quality it is. I guess I would need to empty the well first, since it hasn’t been in use for ages.
You’re welcome. That’s an interesting question, I don’t know how you’d get the water tested unless your municipal supplier will test it for you? Maybe for a fee? We have labs on site at the treatment works where we carry out analysis but that was for instrument verification. For example we’d regularly take a sample, add a reagent and determine the chlorine residual amount. Then you ‘span in’ the instrument by telling it the actual measured value. Instruments drift so it’s important to verify them against a known value. The actual regulatory samples were collected from site and analysed at the main labs at the head office.
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The municipal supplier can do it, but there are also independent waterlabs that can analyse water samples. I have to check the municipal rules first though, I’m not certain I’m allowed to use well water for household purposes when we are connected to the municipal grid… or at least there might be some limitations regarding certain types of use.
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