A water softener is a device which removes the chemicals in hard water areas which cause scaling: calcium and magnesium carbonate. It should not be confused with chemical/electrolytic/magnetic DESCALERS which merely attempt to prevent these chemicals depositing themselves inside pipes, tanks and shower heads. Nor should it be confused with a water FILTER, which removes bacteria, chlorine, pesticide residues etc. The chemicals which cause water hardness are actually removed by a water softener, but the resulting "softened" water is not the same as that in soft water areas, because it contains sodium compounds, as explained below.
Advantages of Softened Water
- More pleasant to wash with: feels smoother; no soap scum; fewer skin problems (from wet shaving, for example)
- No scaling of pipes, kettles, tanks, baths, showers etc.
- Less washing powder, washing-up liquid, cleaning materials etc. required * Tea tastes better and concentrated soft drinks can be diluted more
Disadvantages of Softened Water
- It is not recommended that softened water is consumed by those on a low sodium diet, and for this reason the cold tap in the kitchen is usually connected to the un-softened supply, or a third tap is fitted. There is a long-running debate about the pros and cons of drinking softened water, but sodium carbonate is not a dangerous substance. Softened water should not be used on pot plants either.
- Some people do not like washing with soft/softened water because it is harder to rinse off soap.
Requirements of Water Softeners
Water softeners are fairly bulky, occupying most of a 60cm base unit if they are installed in the kitchen. Manufacturers seem to have put a good deal of effort into minimising the amount of room occupied, however, and there are many different formats. Access is required to add salt, and if a fault occurs (although I am not aware of any routine maintenance being required).
Most softeners require a (low current) electricity supply to operate valves and timers. Kinetico softeners operate entirely by water power.
Softeners require an overflow, with a free fall to the outside, and a drain, which can be a 15mm pipe and doesn't have to have a free fall as it is pressurised. The rising main needs to have a "pi" section of three valves (including a bypass) and a non-return valve to keep the water authorities happy. The softener itself is connected by flexible hoses, and these can restrict the flow rate if they are long.
Kinetico make a unit where the salt cabinet is separate from the rest of the softener. As the salt cabinet needs the overflow and access for filling, and the softener needs the drain and the rising main, this can ease installation in awkward situations.
Softeners do increase your water consumption by a significant degree: the figure for the Kinetico is that it uses 9 gallons for regeneration, after softening between 40 and 70 gallons: a 13-22% increase for a fairly efficient unit. This is in addition to the salt, which goes down the drain in one form or another. If you are worried on environmental grounds you should think carefully (bearing in mind that fewer cleaning materials will be used) if your water is metered you should think very carefully! If you can put up with scale in the toilet bowl, toilets can be plumbed to the un-softened supply. There is no point in feeding outside taps with softened water.
How It Works
Water softeners work on an "ion exchange" basis. The hard water is passed through a resin bed, where the calcium and magnesium ions are removed and replaced with sodium ions. The water will thus contain sodium carbonate. Periodically, the resin must be "regenerated" by flushing with brine. The salt dissolved in brine is sodium chloride, and during regeneration the sodium ions are removed and replaced with the magnesium and calcium ions from the resin bed. The waste water from this operation is flushed down the drain, as is that from "backwashing" which is performed to remove excess brine from the filter. The salt for regeneration is especially made for the purpose and is usually bought in 25kg bags which cost about 7UKP. How long the salt lasts depends on the hardness of the water and the efficiency of the water softener.
The Differences Between Water Softeners
The main differences between water softeners occur in how they go about the process of regeneration. This takes the order of 20 minutes, and during this time the resin bed is unable to be used for soft water. There are two main solutions, which are described below with their variants. To my knowledge there is no softener which actually senses when the resin is exhausted they all either meter the water (having previously been set to the expected level of hardness) or regenerate at a preset interval.
a) Timed Regeneration. The idea behind this is to regenerate while nobody wants to use water (normally in the middle of the night). If the softener only feeds a header tank then so much the better. The cheapest ones simply have an electromechanical timer which initiates regeneration at fixed intervals (Wickes being an example at 399UKP) others (e.g. Aqua Dial) have a microprocessor which estimates by metering the water over a period of days when the filter isn't going to last another day and initiate regeneration that night. Some (Aqua Dial included) also have a "proportional dosing" system whereby they only use as much salt as is calculated to be needed for the state of the filter. This should further improve efficiency.
b) Dual Resin Beds. Water usage is metered, and when one bed is exhausted, the other one is substituted and the first is regenerated. As this can happen at any time, the softener's efficiency is not dependent on the pattern of water usage.
There are also two types of salt: block and tablet. Some softeners can use both. Block salt is easer to handle and is claimed to be more efficient on machines which control the amount of brine to be used for regeneration by a change in level in the brine tank (which I presume does not include machines with proportional dosing). This is because the volume of water for a given change in level depends on how packed together and dissolved the salt tablets are, and is set to the worst-case scenario, therefore usually using an excessive amount of brine for each regeneration. Salt blocks, however, sit on a platform with only their bases in the water, so the volume of the brine tank does not vary.
Also, as previously mentioned, not all softeners require an electricity supply.