The question pertains to the effects of fluoride in the community water supply, specifically the outcomes of consuming water with fluoride concentration of 3 ppm (parts per million).

The options provided describe different health effects related to fluoride levels:

1. Brown mottling of teeth due to excess fluoride exposure: This condition is known as dental fluorosis. It typically occurs when children consume excessive fluoride over a long period during tooth formation, causing changes in the appearance of the enamel. At fluoride concentrations between 1 - 4 ppm, mild to moderate dental fluorosis, which appears as brown mottling or speckling of teeth, is most commonly observed.
2. Loss of tooth enamel due to complete fluoride absence: This is not relevant as the scenario provided involves excess fluoride, not its absence.
3. Severe skeletal deformities due to chronic fluoride exposure: This is a condition known as skeletal fluorosis, which is associated with consuming fluoride concentrations much higher than 3 ppm, generally above 10 ppm over many years. It is unlikely to appear with 3 ppm over shorter periods.
4. Increased tooth decay due to inadequate fluoride exposure: This would be the result of fluoride deficiency, leading to the absence of fluoride's protective effects against tooth decay, but again, not relevant here where there is excess fluoride.

Given the fluoride concentration in the water supply at 3 ppm, the most likely health effect to appear first among long-term consumers is brown mottling of teeth due to excess fluoride exposure, i.e., dental fluorosis.

Thus, the correct answer is:

1. Brown mottling of teeth due to excess fluoride exposure