Short answer: You can run a waterjet on tap water, but you will pay for it in dramatically shortened component life. For any production environment, treated water (RO or DI) is not optional—it is economic necessity.

What Happens with Untreated Tap Water

Tap water contains dissolved solids (calcium, magnesium, silica, chlorides) measured as Total Dissolved Solids (TDS). Typical tap water ranges from 100–500 ppm TDS. When pressurized to 60,000 psi, these minerals behave like abrasives themselves:

A set of high-pressure seals that lasts 500 hours with RO water may fail at 200–250 hours with tap water. An orifice that runs 60 hours on RO might fail at 30 hours on tap.

Water Quality Standards by Application

Why RO is the Industry Standard

Reverse osmosis removes 90–95% of dissolved solids. A typical RO system for a waterjet includes:

• Sediment prefilter (removes sand, rust)

• Carbon filter (removes chlorine—chlorine attacks seals)

• RO membrane (removes dissolved minerals)

Output quality: 10–30 ppm TDS, neutral pH (6.5–7.5)

Cost: $1,500–$4,000 for a system sized for 1–3 gallons per minute

Operating cost: $0.20–$0.50 per hour (membrane replacement every 2–4 years)

Is DI Water Better Than RO?

Deionization removes nearly all ions, producing 0–5 ppm TDS. However, DI water is aggressively hungry for ions—it will leach minerals from metal components, potentially causing corrosion in some pumps. For this reason:

• Most pump manufacturers recommend RO (10–30 ppm) over DI (0–5 ppm) for standard pumps

• Ultra-high pressure pumps (90,000+ psi) often require DI because any remaining solids cause rapid orifice wear

• Mixing RO and DI (RO then a DI polishing cartridge) produces ultra-pure water for critical applications

The Hidden Problem: Chlorides and pH

Tap water often contains chlorides (from municipal chlorination) and variable pH. Both are problematic:

Tap water can be within all these ranges (some municipal water is excellent) or disastrously outside them. Testing is the only way to know.

The True Cost Comparison

Scenario: 50 HP intensifier running 2,000 hours per year

The RO system pays for itself in 3–6 months through consumable savings alone—before considering reduced downtime from fewer unexpected seal failures.

Acceptable Short-Term Exceptions

Running on tap water is acceptable in these limited scenarios:

1. Emergency completion of a critical job – One shift (8 hours) of tap water will not destroy your pump, but change back immediately.

2. Very low usage (under 200 hours/year) – If you run the waterjet twice a month for hobby or prototype work, the extended consumable life from RO may not justify the $2,000 system investment. However, you will still replace seals and orifices more often.

3. Exceptionally good tap water – Some deep well or mountain sources produce water at 30–50 ppm TDS naturally. Test first. If TDS is under 50 ppm and chlorides under 30 ppm, tap water may work acceptably.

What About a Water Softener Only?

A water softener replaces calcium and magnesium (hardness) with sodium. This prevents scale but does NOT remove chlorides, silica, or total dissolved solids. Softened water typically still has 200–400 ppm TDS.

Result: Better than raw hard water (less scale on fittings) but still far worse than RO for seal and orifice life. Softeners are a pre-treatment step before RO, not a replacement for it.

Final Recommendation

Do not gamble on tap water. The $2,000–$4,000 investment in an RO system is the single highest-return accessory for any waterjet. It pays for itself faster than a better pump, a larger table, or almost any other upgrade. Running tap water is like using dirty oil in your car engine—it works for a while, but the repair bill will far exceed the money you saved.