Thanks for your informative post. I do recognize that a small Brita filter system may not be the highest specification option, and I hadn't even considered Brita domestic filters until Trevor's mention. I already own one of the particle filters (the Ametek AM1), so I'm looking at the further options when deionized or distilled water is suggested or needed.
On the Brita filter: What processes are you using the Brita filter water for, and how many litres do you get before the cartridge needs to be changed?
On the lab deionizer: Approximately how many litres of water can be processed per £40 cartridge?