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I'm considering buying a water softener, but I heard that they waste a lot of water, and I don't really want my water bill to skyrocket.

I haven't been able to find any clear indication of how much water water softeners waste. They generally have specifications that state the amount of water used for regeneration, but I don't know how often regeneration happens.

How can I tell by the specifications of a given water softener how much water it will waste?

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4 Answers 4

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You can easily calculate how often regeneration will be necessary if you know how hard your water is. If you are using city water, they should be able to tell you otherwise there are kits you can use to test your water. And any softener salesman should test your water as part of sizing your system.

In my area, the hardness is measured in grains per gallon and the value is 10.

My water softener is rated at 30,000 grains so I need to regenerate after using 3,000 gallons of water. I use about 100 gallons per day so I regenerate every month.

This link gives you an idea of how much water is used during regeneration: http://www.watervalue.com/softener_regen_water_usage.html

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Basically, water softeners contain a filter with a chemical that attracts positive ions (like the alkali metals calcium and magnesium). The filter is originally "charged" with sodium ions using the salt you put in the bin. Run hard water through it, and the calcium and magnesium compounds (mostly carbonates) are converted to sodium carbonate, which doesn't cause scaling. The magnesium and calcium remain in the filter media.

Regularly, the filter must be "recharged", the magnesium and calcium in the filter are flushed out by pumping very salty water through the filter. The sodium from the salt replaces the calcium and magnesium in the filter media, which then bond with the free chlorine and hitch a ride down the drain as relatively harmless chlorides.

This process does require quite a bit of water - up to 25 gallons per recharge is the figure I found. However, you have to ask what's more expensive, flushing a few gallons a day through the filter to keep the sodium and calcium out of your plumbing, or calling a plumber to flush a corrosive and poisonous chemical through your pipes to dissolve the scale, then flushing even more water through the pipes to rinse them out so the water is usable again? Not to mention the extra chemicals you'd use with each load of laundry and dishes to keep your clothes from becoming stiff and your dishes free of spots (some of which contain environmentally-harmful phosphates), and the filters you would need to install on faucets and in fridges to clean your drinking water.

There are different systems for determining when to do this admittedly costly recharge cycle. Most of the cheaper ones do it on a schedule which can be programmed based on average demand; every night, every two nights, depending on how much water you normally use each day. Others can sense the sodium content in the filter media and recharge when the sodium is exhausted. Still others simply measure water usage and "know" that a charged filter can soften X gallons. They all have pros and cons, the main tradeoff being price for water efficiency, but some will also recharge any time it's needed, which may be when you need your water (the softener cannot provide soft water, and sometimes can't provide ANY water, during a recharge).

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I'm not sure if "waste" is the correct term. They need to backwash some water through them in order to remove the hard materials ("regenerate") they have removed from your water; it's a necessary evil of the process. It is however not just running water for the sake of it.

How often this process runs will depend on how much water you use and how hard your water is to begin with. If your water isn't all that hard, then it might not run at all unless you are filling a swimming pool daily. On the other hand, if you have really hard water, it might not take that much usage before it needs to regenerate.

I don't think the usage will cause your water bill to skyrocket, it's probably less than a single shower.

The specifications might give you a general idea of what to expect, but it will always depend on the softener usage.

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In the western states that are undergoing drought at this time, waste is the proper term. –  Fiasco Labs Jan 28 '14 at 15:54

I did some significant research on water softeners a few years ago. I did not find numbers for exactly how much water they use when the regenerate. However, there are multiple systems to determine when they regenerate. This can make a big difference on how much water is used.

The simplest and cheapest models just have a timer for when they regenerate. This can result in regeneration when it is not needed. It can also result in the water getting hard because the system does not regenerate fast enough if you use a lot of water.

There is also a metered system where you use a formula for your typical daily usage and the hardness of the water. You set the meter to regenerate on a particular number it it regenerates when necessary.

There are more complicated electronic systems that monitor water inflows, outflows, hardness, etc. and regenerate exactly when needed. Some of these systems have two tanks, so you always have soft water. I was told by multiple people that the electronic systems are not as reliable as the old fashion mechanical meter models. The cost savings over time are also not worth the additional cost of the system.

I ended up choosing the metered version. It was recommended to me to get a softener with a Fleck brand valve. I have had it for a couple years and have no trouble with it.

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