Pure water filtering

[Vijay]

Hi all,

Looking to try and produce pure water for washing windows and cars. Anyone know if it's possible to filter water to get "pure water"

Vijay

[countrypaul]

Short answer is no.

If you dissolve simple things like salt or sugar into water they are impossible to filter out since they are efectively to small. It is possible to filter out some of the water using a semi permeable membrane in a process call reverse osmosis - but this is usually quite expensive. Dissolved ionic compounds can be removed using ion-exchange resins, these effectively replave metals with hydrogen ions and ions such as sulphate, carbonate, chloride with hydroxide ions so the two ions used make water.

Non ionic compound can often be absorbed onto things like activated charcoal (as found in domestic water filters.

So combining a number of methods will produce much purer water.

How pure do you need it for window washing?

[dgs]

We used to have demineralised water on tap in the labs at ICI, would this have been filtered through ion exchange.

[Vijay]

Don't really know how much I'll need, I'd hazard a guess of 25-50l maybe?

Would using rain water make any difference?

[countrypaul]

Demineralised water can be de-ionised water since most dissolved minerals are present in solution as ions. In industry large boilers tend to use de-ionised water. Before university I worked at a chemical plant on Teeside where they used de-ionised water through the boiler, two large tanks of ion exchange resin, probably 15ft high and 10ft wide, one for cation and one for anion exchage. I remember testing the boiler water for oxygen levels usually zero, and also hydrazine levels - of there was any present then the oxygen level should be zero as it usually was.

Rainwater is likely to have a fairy low level of mineral content depending on what it is collected from, but can have quite high levels of organic matter (think moss etc on roofs along with bird poo etc.)  I would expect most organic matter could be removed with an activated carbon filter. 

This gives a fuller explanation: https://blog.veoliawatertechnologies.co.uk/what-is-deionised-water

You can buy deionised water in various quantities, from about £2 for 5L upwards, £175 for 1000L IBC for example.

Maybe the simplest way forward is to test some samples on a window (or windows) and see which are acceptable, try tap water (are you in a soft or hard water area?), some purchased de-ionised water (5L), and the results of using an activated carbon filter - if need be, use a Britta type jug filter (should be good for maybe 100L depending on your water).

[Tony]

From pyro Steve:

"I see someone was talking about pure water on Bio powered, get them to look at a company called ‘spotless water’ as it is a company who have outlets all over the country where you pay about 4p/L for pure water. It’s self service where the window cleaning boys go for their water. I’ve had some (for the WI) and it’s dead easy to use.
Hope it’s suitable for his needs, as it saves all the hassle."

[Vijay]

Thanks guys.

I think buying from Spotless Water might be the easiest way to go