TDS Meter with LCD Display. TDS meters measure Total Dissolved Solids in water.
TDS meters can are helpful for brewing if you’re using a RO filter or if you purchase RO (reverse osmosis) water for brewing. If you’re using an RO filter a TDS meter tells you how effective your filter is and can help you know if your filters need to be replaced. If you buy RO water, a TDS meter can let you know what you’re getting as some water processors add minerals back for flavor. A TDS meter will allow you to make sure you’re getting what you want.
RO water can be built up to reflect the exact water profile you’re looking for. See: Water by John Palmer and Colin Kaminski
TDS Meter Digital Water Tester, DUMSAMKER Professional 3-in-1 TDS, Temperature and EC Meter with Carrying Case, 0-9999ppm, Ideal ppm Meter for Drinking Water, Aquariums and More – note that multiple variations of this product may be available, as such a different version may appear at this link
Also: Portable Universal 5-stage Reverse Osmosis RO Purification Water System with DI Deionizing Mixed Bed 0PPM postfilter, made in USA – [Review]