SELECT
    samples.id,
    samples.wet_weight / samples.dry_weight - 1 AS percent_water,
    100 * percent_water AS percent_water_100
FROM samples;

SELECT
    s1.id,
    s1.percent_water,
    100 * s1.percent_water AS percent_water_100
FROM (
    SELECT
        samples.id,
        samples.wet_weight / samples.dry_weight - 1 AS percent_water
    FROM samples
    ) s1;