First, is it a clear bowl where you can see separation? It is still tough for me to see on my Kubota but when the engine dies it is time for servicing. I have a water separator on my transfer tank. The instructions on it say change the element when the fuel flow drops to an unacceptable level. That appended quickly - one tank filled fast and the next tank took forever so I replaced the element and was back to normal. I couldn't see visible water in the clear housing. When my tractor has died due to water I couldn't see any visible difference in the bowl but when I removed the bowl I spilled some fuel on a flat shield on the axle and the water puddled separate from the fuel. That was the only way I was sure my problem was water and not dirt. Over 50 years now working on diesels and I have never clearly seen a line in the separator where I could definitely say this on top is the fuel and this on the bottom is water. Yet I have pictures from some injection pumps with rusty internal parts where enough water has made it past the separator to cause the rust. The best separators I have seen have a water sensor but when I wanted to have them added as standard equipment I got vetoed due to cost.