Choosing the right Sterisil Straw comes down to two questions:

What is the TDS of your source water?
Do you want a 90-day or 365-day straw?

One important point: having municipal water doesn't automatically mean you need a Municipal Sterisil Straw. The correct straw is determined by the Total Dissolved Solids (TDS) of the water going into your dental unit.

Which Sterisil Straw Do I Need?

According to Sterisil:

0–100 ppm TDS: Distilled Straw — S90 or S365
101–250 ppm TDS: Municipal Straw — S90m or S365m
Over 250 ppm TDS: Use distilled or distilled-quality water with a Distilled Straw.

These ranges come directly from Sterisil's current Instructions for Use.

Why Testing Your Water Matters

In North Star's field experience, we've encountered municipal water supplies in our service area that fall outside the range specified for the Municipal Straw.

That's why we recommend checking your TDS instead of choosing based on whether you have city water.

A handheld TDS meter can test the water being supplied to your dental unit. You may also be able to obtain information from your local water provider.

For offices with source water above 250 ppm, Sterisil recommends using distilled or distilled-quality water with a Distilled Straw.

90 Days or 365 Days?

Once you know which water formulation you need, choose your replacement interval:

S90 — Distilled, 90 days
S365 — Distilled, 365 days
S90m — Municipal, 90 days
S365m — Municipal, 365 days

For practices that prefer fewer changes, the 365-day option provides a convenient once-a-year replacement schedule.

Don't Forget Waterline Testing

The correct straw is only one part of dental unit waterline management. Sterisil recommends regular waterline testing, including quarterly testing, to verify that your protocol is working as intended.

North Star's Take

Don't choose a Municipal Straw just because you have municipal water. Check your TDS first.

0–100 ppm → Distilled
101–250 ppm → Municipal
Over 250 ppm → Distilled/distilled-quality water + Distilled Straw

We've seen firsthand why that distinction matters, and a quick TDS check can help make sure you're buying the right product from the start.

Not Sure Which One You Need?

Send North Star your TDS reading and we'll help you choose the appropriate Sterisil Straw for your practice.

Clear direction for your dental practice.