No it's not due to hard water as I have soft water and some of mine bobble. I find it is mostly garments which have artificial fibres in them. My 100% cotton tee shirts never bobble although my Lambs wool cardigan does but as it is so soft and cuddley I just defuzz it from time to time. My winter coat which is 90% wool bobbles slightly and in twelve years it hasn't even been drycleaned let alone washed, just well brushed and always hung on a coat hanger. If the bobbles bother you get one of those battery powered de-fuzzers. They really work.