Demineralized Water in Conservation and the MINIDEM 30

Demineralized Water in Conservation: Why It Matters, How to Measure It, and How to Produce It in the Laboratory

In conservation, water is everywhere: cleaning, poultices, solution preparation, and rinsing. Precisely because of this, it can become one of the greatest threats to an artwork. Tap water contains dissolved salts and minerals that can be deposited onto surfaces, leading to efflorescence and often irreversible damage. The solution is demineralized water—but "demineralized" does not mean just one thing.

There Is No Such Thing as "Demineralized Water": There Is Conductivity

There are many grades of demineralized water, and what distinguishes them is conductivity, measured in microsiemens per centimetre (µS/cm) using a conductivity meter. The lower the conductivity, the fewer dissolved salts the water contains. A chemical laboratory may require extremely high purity levels, which are expensive because they quickly consume production systems; for conservation work, however, the important thing is to identify the right threshold for the specific application. This is the first question to ask yourself — and your supplier — before choosing a system: what conductivity does my work require?

The critical point is that "exhausted" water cannot be recognized by sight: it looks identical to pure water. Without a continuous monitoring instrument, mistakes are just around the corner.

Reverse Osmosis or Ion Exchange Resins?

Demineralization systems are divided into two main families.

Reverse osmosis systems are unbeatable when large volumes of water are required continuously — for example, for washing and desalinating marine archaeological finds. However, they are complex and expensive systems: the osmotic membrane must operate continuously, not "on demand." For a conservation laboratory, they are almost always oversized.

Ion exchange resin demineralizers, on the other hand, work exactly as required in a laboratory: open the valve, produce the water you need, close it. They are more flexible, easier to use, and simpler to maintain. This is the technology behind the MINIDEM line.

MINIDEM 30: Pure Water, Under Control, Wherever You Need It

The MINIDEM 30 is CTS's professional trolley-mounted demineralizer: a stainless steel column filled with 30 litres of high-capacity mixed-bed ion exchange resins (cationic/anionionic), mounted on a stainless steel frame with standard wheels — an exclusive feature of this model. You can move it wherever it is needed, in the laboratory or on site.

Its operation is straightforward. Water enters through the FP5 mechanical pre-filter (5-micron cartridge, transparent housing: when it becomes clogged with limescale and dirt you can see it, unscrew the housing and replace the cartridge), passes through the resin bed, and then flows through the LED conductivity meter, which continuously measures water quality: green light from 0 to 20 µS/cm, red light above this value. No interpretation required, no human error.

The inlet and outlet connections are quick-connect fittings: installation requires neither a plumber nor any special expertise.

The figures: flow rate up to 420 litres/hour, purity down to 1 µS/cm, maximum inlet pressure 5 bar, indicative operating capacity from 4,000 litres (20°F water hardness) to 2,500 litres (34°F water hardness). Compact dimensions (31 × 30 × h.107 cm) with a weight of approximately 37 kg.

Five Tips to Make It Last (and Perform at Its Best)

1. At first start-up, the LED is red: this is normal. The new resins need to become activated — discard approximately the first 50 litres and the light will turn green.
2. Do not use it like a tap. Every activation engages the resins: many small, frequent withdrawals significantly reduce the operating capacity. Planned production cycles are preferable.
3. Keep the pressure under control. Even below the 5-bar limit, water flowing too quickly through the resins will leave the system with lower quality.
4. Know your water. Hardness varies from one area to another (which is why operating capacity ranges from 4,000 to 2,500 litres): an analysis of the incoming water will tell you what to expect. Also pay attention to plumbing work, which may temporarily introduce dirt into the incoming water supply.
5. Keep a spare column available. Resin regeneration takes weeks: with a pre-filled spare Model 30 column, you will never run out of pure water. CTS also supplies 30-litre mixed-bed resin packs and supports resin replacement — which must be carried out carefully: improperly filled resins mean a permanently red conductivity meter.

MINIDEM 20 or 30?

The two models share the same technology: what changes is the column capacity. If you work with materials that require large amounts of water — archaeology or paper conservation — the MINIDEM 30 is the right investment: the price difference is modest, the 420 l/h flow rate is designed for laboratories with intensive operations, and it is the only model supplied with a trolley as standard.