DI water "on tap"?

[Beatsy]

I currently use between 20 and 40 litres of DI water a week. I am pretty stingy with it and use tap water whenever I can substitute, although that adds time and extra steps to processes associated with cleaning diatoms.

I'm stepping up the amount of diatom cleaning I do, a lot. With current usage patterns (and still being stingy) I'd easily exceed 50 litres a week for a year or more. I want/need to be able to use much more DI water and use it freely without concern for costs or amount left. In short, want to be able to splash it about like, umm, water! Let's say twice as much as I use now for any given process - so possibly up to 100 litres a week.

To that end, I started researching water purifying systems to make my own DI water from tap water. There are lots and lots of options and I've got a bit bogged down in it all. I wonder if anyone here can help me pre-narrow my options so I don't have so many different (and new to me) systems to evaluate and choose from?

The resin filtration systems look favourite for sure. Not ones with replaceable cartridges (just a cash cow for the manufacturer to milk) but the ones that can be homemade, you just buy large bags of the special resin beads to fill it and replace when spent. However, I also found out that the resin lasts longer if the water is pre-filtered by a membrane system to lower contaminants below 10ppm before feeding through the resin. This part seems to be a relatively high-pressure affair and might require an electric pump - which I'm not too keen on. I'd rather have a manually pressured system to make batches of DI water (for storage in large tapped containers). As I said, there are so many options, I've got a bit lost. Here's my list of requirements, I'd really appreciate it if someone could help me narrow down what *kind* of a system I need to put together to meet them. Kit and consumables need to be readily available in the UK too. Thanks...

1. Produce up to 100 litres of 0-1ppm DI water a week.
2. Cost much, much less than 50p/litre (current price with Halfords DI water). I am expecting it to cost pennies a litre, but I'd like to include the cost of the setup and consumables (resin), amortised over 2-3 year's to judge the overall cost/litre compared to buying retail.
3. Purity down to zero ppm is ideal and achievable but 1-2ppm works fine for my applications - the same rating as the Halfords DI water. Our tap water is quite hard, but I don't currently know the actual ppm value (no meter yet).
4. It would be nice to have a system that just produced DI water as it was needed, from a tap, but I think I'd prefer a batch system for space and positioning reasons. I'll fill two or three 20-litre containers at a time and tap into those for daily use. I suspect this will be the cheapest and easiest to implement and likely the most practical for me - so let's go that route (only).
5. Happy to make stuff myself, but also happy to buy a pre-made, fully working system/product if such a thing exists. I would prefer a manually operated system (no electricity needed) if possible. The pressure needed in the membrane part of the system will probably determine if that's practical though. Very unsure about this part - but would go the electric pump route if that's necessary. I'd (probably) prefer to buy a complete ready-made product for that part if it is needed though. Maybe it's possible to go with resin filtration only and take the hit in the reduced lifetime of the beads. Buying more of them could still work out cheaper than buying a membrane pre-filter system insted? I don't know enough to guess...
6. Did I forget any important requirements?

Phew. Sorry for the long ramble. Thanks for reading, and thanks in advance for any and all advice...

[Smokedaddy]

Just curious why not distilled water?

[Beatsy]

Just curious why not distilled water?

Far more expensive, and in my experience strewed diatoms stick terribly to the glass if they were suspended in distilled. Three times worse in triple-distilled too - honestly, not joking. Never so with DI water.

I did read a couple of passing references to pure distilled water doing something like this to silica - but never got details as it was all behind a paywall. I haven't been able to find the abstracts since either.

[Smokedaddy]

Like I said, just curious. When I was researching off-grid 'stuff' for my home in the mountains I read about atmospheric water generators and DIY water distillation systems.

[Ichthyophthirius]

Just a quick question: Have you tried rain water collection? I remember aquarists using rain water (ideally off a plastic or glassed tile roof) for soft water fish before reverse osmosis units were around.

If you contact a local aquarist society, maybe someone would be willing to supply you at a good rate? 100 l is in the order of magnitude for the daily production of one of these units. Just had a look at an aquarist classified adds site; seems to be common practice with lots of people looking for and selling RO water. http://www.aquarist-classifieds.co.uk/p ... _water.php

Regards, Ichty

[Lou Jost]

I used a reverse osmosis system to get pure water for my orchids. Tehy needed many gallons per day, maybe twenty or thirty. It worked beautifully. These systems are a few hundred dollars and with proper care and pre-filtering they last many years.

[palaephatus]

You may consider using a dehumidifier.

During the non-winter part of the year I run one in my basement, a cheap model with a price tag of approx GBP 60 on sale. The model is compressor based (R134a refrigerant), uses some 300W of electricity and provides approx. four litre of water/day. The running cost, while not negligible, is a cheap way of having a dry mechanical workshop.

It is possible to acquire a small DI- or RO-system, however, they do take some maintenance. The water reservoir of the dehumidifier does take some cleaning for bio-film from time to time.

If distilled water is to pure, one solution could be to add a controllable background of a suitable salt. The standard way to ascertain water purity (from salts) is to measure the conductivity. Sensors for e.g. pH and conductivity can found surprisingly cheaply from Chinese suppliers on-line - less than 5 GBP for a pH-electrode.

Kind regards

Palaephatus

[EricRed]

I would encourage you to consider a continuous feed still. Figuring out when to rebuild your DI column and having to do it seems like a pain. In the dark ages when I was a chemist, our lab only used DI water for basic use (washing glassware). We redistilled it for serious stuff. The DI system had electronics that indicated when to replace the filter. I don't know if it was based on volume or measurement of output quality.

An eBay search came up with continuous feed stills for less than US$500 including shipping from China with the capacity you looking for. Downside is they have pretty heavy duty electrical requirements, but once running, the only thing you might have to do is descale it once a year.

I have an old Sears still that makes about four liters in a batch. I figured it costs about US$0.25 a batch.

Just an idea.

Eric