[billozz]

we currently use an r/o system which fills a 650ltr tank overnight, this is not quite enough water for us and we could do with a little extra for most days but occasionally it would be nice to have water on demand, for a school etc. we have heard that you can use just d.i cylinders and pump tap water through them to produce pure water, but we are unsure of the costs involved my tap water is about 70 tds which i believe is quite low could anyone suggest a way in which we could continue to use our r/o and utilise a cple of d.i cylinders to finish off a days work or a school or large contract etc. or would we be better off swopping striaght over to a d.i system
thanks in advance
Bill

[Alex Gardiner]

The simplest way of sorting this situation out would be to fit a permanent large DI pressure vessel (14 litres etc) after your tank in your vehicle.  When using pure water from your RO system, you will not wear out your resin at all.  When you get to the end of a day all you have to do is fill the tank with a hose pipe with ordinary 70ppm water and the DI unit that you have permanently plumbed in will automatically purify it for you.  The next day you simply fill back up with purified RO water. 

To give you an idea how long the canister would last, if using a 14 litre canister you should get in excess of 4000 litres of purified water from 70 ppm input water.  If only using for the last 100 litres of the day, this would last you in excess of 40 work days.

[vwm]

what is the formla with di resign so we can work out how per litre of di will last

[Alex Gardiner]

This is the formula for a very conservative guide to how many litres of water you will get (please note this does not take into account the shaking of DI vessels to rejuvenate the resin which can significantly extend the life of it):

500,000/tds of your water=number of litres of pure water from a 25 litre sack of resin

[vwm]

thx alex

[billozz]

The simplest way of sorting this situation out would be to fit a permanent large DI pressure vessel (14 litres etc) after your tank in your vehicle.  When using pure water from your RO system, you will not wear out your resin at all.  When you get to the end of a day all you have to do is fill the tank with a hose pipe with ordinary 70ppm water and the DI unit that you have permanently plumbed in will automatically purify it for you.  The next day you simply fill back up with purified RO water. 

To give you an idea how long the canister would last, if using a 14 litre canister you should get in excess of 4000 litres of purified water from 70 ppm input water.  If only using for the last 100 litres of the day, this would last you in excess of 40 work days.

alex,
the problem i see with this idea is that we do not use all of the water that is in the tank, simply because the outlet is a little above the bottom of the tank, if we fill up with tap water will this not contaminate the water that goes in the next day via the r/o

[D.Salkeld_Ltd]

Alex,

Thanks for the formular.  I have done a little spredsheat calculator to enter input TDS and amont of resin and it gives amount of pure water.

David

[macmac]

The simplest way of sorting this situation out would be to fit a permanent large DI pressure vessel (14 litres etc) after your tank in your vehicle.  When using pure water from your RO system, you will not wear out your resin at all.  When you get to the end of a day all you have to do is fill the tank with a hose pipe with ordinary 70ppm water and the DI unit that you have permanently plumbed in will automatically purify it for you.  The next day you simply fill back up with purified RO water. 

To give you an idea how long the canister would last, if using a 14 litre canister you should get in excess of 4000 litres of purified water from 70 ppm input water.  If only using for the last 100 litres of the day, this would last you in excess of 40 work days.

alex,
the problem i see with this idea is that we do not use all of the water that is in the tank, simply because the outlet is a little above the bottom of the tank, if we fill up with tap water will this not contaminate the water that goes in the next day via the r/o

Yes, but the resin vessel will still purify it. a bit of 70tds water mixed with your normal RO water won't make hardley any difference to the resin life. Alex's suggestion is spot on. The other way to do it would be to just carry a seperate 11Ltr DI vessel in van & use it straight from the outside tap.
With a tds input of 70ppm your resin will last for quite a while.
Doing either what I or Alex have suggested gives you the best of both worlds (an ideal set up). RO water mainly with pure water on demand when needed.

tony

[JM123]

a little tip if I may - if you want to finish a job/s with tap water then if at al possible top up before you run out, this way the concentration of tds of the water is lower, although you are still passing the same amount of tds through the resin its easier on the resin because its less concentrated.

maybe i've just confused you

[Ian_Giles]

As others have said...can't add much, except that should you need to top up to finish off for the day, only put enough tap water into your tank that you actually need.
So at least whatever is left in your tank is going to be minimal, and if it is 100% tap water, well, you can always empty it down the nearest drain and start the next day with a tankful of unsullied pure water.

Ian