Carbonating water can be done in three different ways. You can work the acid in to the water by shaking it and you can let time do the work for you or you can increase the carbonic acid amount and then let a portion of the acid evaporate. With a Ritchie carbonator and similar devices you add carbonic acid to water or even to wine and other beverages, something that cannot be done with a soda machine. This process entails carbonating, waiting, carbonating some more, and so on however this process is too difficult and lengthy when you just require a refreshing drink.
This video shows how to carbonate water using a home-made machine in a soda-bottle. After pressurizing the carbonic acid is shaken into the water.
This is fine, as carbonic acid costs next to nothing in large CO2-bottles however the smarter way is by utilizing over-pressure as this requires no waiting or shaking.
All commercial soda machines use over-pressure and as carbonic acid is more solvent in cold water, it is best to use your refrigerator to cool it first.
An especially strong PET bottle is partially filled with water as room is needed for pressure equalizing similar to that of a purchased PET bottle.
You then add carbonic acid until you hear the pressure valves release and then release the button allowing the pressure to equalize. If you require more carbonic acid you can easily repeat these steps quickly learning what level of carbonation tastes the best for you personally. Then taste can be improved even more with adding flavor for carbonated water.
Here is a German video that shows how to carbonate water using a Sodastream with the carbonated water being immediately ready for either drinking or flavouring.
This is the best and easiest way as the bottle is stronger than normal and should last for many years.
So why are there home-made machines? Simply to reduce the price of the carbonic acid.
The acid itself is virtually free with some companies supplying five, ten or fifteen kilos for the same price. What you actually pay for is not the acid but the work involved in refilling bottles including a small mark-up. Refilling bottles of 2 kilograms upwards which is usually required for restaurants and other small businesses usually costs about 20 Euros making the average price for a litre of carbonated drinks only a few cents.
The Carbonic acid you buy for a soda machine is quite cheap costing about 10 Euros per refill which averages out to less than 20 cents per litre. As you can see, this is very cost effective when compared to purchased soft drinks. However when compared to actually using larger acid bottles, 10 Euros per refill or more than 20 Euros per kilogram of acid is quite expensive.
This is why many people see this as excessive pricing and make their own soda machines so that they can utilize bigger canisters.
The soda machine producers on the other hand will make every effort to protect their golden goose. They do this through making the customer sign different contracts and legal documents so that each producer has a monopoly on refilling their own bottles. If they were smart, they would allow refills by any company whuch if marketed properly would lead to many more sales of their base machines.
During the 1980’s one could get refill at Partymans store in Malmö in Sweden for free if you purchased three bottles of aroma. The refills where supplied by Sydbrand at reasonable and competitive prices. Sodastream consequently sued Sydbrand for trademark infringements leading to years of legal action at great cost.
Today, every soda machine producer tries to stop others from refilling their branded canisters using every legal means possible. All this even though in truth a customer can easily refill a bottle in 20 seconds while waiting in a store. This was done by a business in Germany who in turn were also attacked by Sodastream or Soda Club as they are called in Germany,
But Soda Club, or rather Sodastream lost this legal battle. In trying to stop a minimal amount of competition has allowed the opening of totally free competition. This in turn should result in free competition in all EU countries based on current EU legislation. This however will require a company daring to challenge Sodastream or by authorities taking action based on consumers who are no longer willing to accept the status quo.
Instead of making their own home made machines I think people will use the many excellent machines currently on the market such as Sodastream (specially the Sodastream Design) or Wassermaxx. Carbonic acid will be cheaper through refilling the acid from larger bottles themselves or through hooking larger canisters directly into their soda machine.