There is no law in CA prohibiting this that I know of. Your CC&Rs would have to be amended to allow that. Your existing rented units would probably need to be grandfathered in. 
 
I don't think this is a good idea generally. There is no evidence that they use more water than other tenants. What if you have one student renter vs. a family of 5 who owns.  
 
If they brake rules you need to deal with it just like any other violation. You can't say they put a burden on you to enforce rules because that's your responsibility as a board member. 
 
If you start charging fees owners will simply increase their rent amount, which could make your property to high to rent which in turn will result in delinquent HOA assessments and possible foreclosures.

I have my condo en San Diego ,CA, the yard is a mess, I talked The President of the HOAto hire a gardener,sent a letter complaining but to no avail. what can I do?

Does your association employ a management company or you self-managed? 
 
You might research the costs to make improvements you desire.

Thanks to Jeff Ross for his response. I had heard that charging more to an owner who rents his unit would be considered "discrimination" but no one can give me a citation to the law. The charge be considered a fee rather than an increase in HOA dues . We suspect there is higher water use because our water bill went up after these tenants moved in. We already live in a high rent area and an extra $100 a year wouldn't bother the students who share the rent four ways.

Louise, it wouldn't be discrimination if you apply it to ALL landlords. You can't pick and choose. Meaning every single landlord in your condo must pay the same 'fee' when they rent. They would also have to pay the same fee if the unit is vacant but still available for rent. If tomorrow you have a single person renting their landlord would pay the same 'fee' as one with four students sharing. 
 
How big is your building? I suspect it will not be an easy win as CC&R amendment must be approved by all owners, not just your board. Depending on your bylaws it might required 2/3 of members voting for it or sometimes over 1/2. 
 
I would't recommend doing this and this starts a slippery slope for your association. 
 
What if you have a family of 5 buying a unit? your water bill will go up too and you can't penalize them for it. What if someone uses pool more than others do you charge them for extra chlorine? 
 
Depending on your building configuration you might be able to install separate water meters for each unit. You might save a lot more that way. When all owners know that they are paying for their water the will save more.

Thanks again for your advice. For the record, our condo is not a building but a group og individual townhouses. We thought of putting in separate meters but it woukd be very costly and we don't think we'd get it passed by the members. Our CC&Rs require that 75% of the owners must agree to a change in the bylaws. Thanks for the point about charging all landlords. We have a few resident owners renting out a room to a single tenant and we weren't going to charge them the rental fee. Your suggestions will be brought to the attention of our board.

Perhaps you could try to handle this directly with the tenants. Is it in the bylaws that you are required to pay for water? If not, have the tenants pay for it. That is one way to cut down cost.

@ Louise: You mentioned "...a few resident owners renting out a room to a single tenant..." Is that arrangement an owner renting one room as opposed to two renters living there? Our by-laws prohibits renting of a single room. Of course we cannot question the living arrangements so we don't always know...however we can control the number of cars. When a lease comes before the board, and there are going to be two renters, then both names appear on the lease and two parking stickers allowed. In our township there can be no more than two non-related people living in a leased unit. We did have a vote of 75% to conform with the township.  
 
In addition, our township requires that all rental properties register and pay $100 to the township every two years. We are working on amending rules and ask that a $200 admin fee be collected for any new leased property, and $100 thereafter on a yearly basis. We have 152 condos and because some of the owners live in other cities, the management company ends up with time-consuming jobs. Currently we have 22 rental units plus parents (approximately 10) who bought the unit so that their student child could live there. Here's another problem -- the child takes in a roommate. Should there be a leased imposed. Earlier we had an owner's son living in the unit, then he started having two and three friends stay around for the 9 month school semester. Then the following year two or three more. Then the son moved out, no lease -- it was a sticky situation. 
 
Any helpful hints or ideas on how we can cut down on renters. Our Association is made up of primarily "Lifers." Owners who have been here for 15-20 years, and who take pride, follow the rules and regulations, pay on time, etc., and in return expect quite evenings, nice behavior at the pool, etc. And it seems now that there are so many "...there goes the neighborhood!" (kidding)

Since the owners pay condo fees they can rent out their unit without paying additional fees. However,they are responsible for anything that needs repair if they own the unit.As for the water and trash they are paid out of the condo fees to the city that provides these services. The tenant pays their PG&E and gas.Any damages that are outside are paid for by the association. As for cutting down on renters it is is hard to do because I, as assistant manager am the only one who owns my own unit here.We have 30 units. Believe me it is a job keeping things looking good and we have plenty of help. I have owned my unit since 1992. All I can advise is to be very careful whom you rent to and run a check on them.I have cleaned and painted nearly every unit here and have only seen one, just one in all my time here that was left perfectly clean and ready to rent, nothing to do.People have bought units only to sell them at some point. It is hard but at least most of the tenants are long term.I do not have any real problems I cannot solve but one has to stay on top of things.The association president really helps me as it can be a real job.I an inundated with tenants coming by and have to to take care of whatever it is they need.I do enjoy the work which is a good thing. If I cannot solve a problem I can the help I need.

If your ccr or the master plan at that time allowed this, then it can happen. if it is no where in any of your plan documentation of paper works you sign or stated anywhere and no other off site owners pay this why would you have too. I would think then it is not correct of paying rental fee to management company, but what do I know.

I have never heard of charging an owner an extra fee just for renting out his unit. It is his or her unit after all. They must still pay condo fees and are responsible for any needed repairs. It sounds like something someone made up just to get more money. If something is yours then why pay an extra fee? ridiculous.As for the water usage,how much is too much by the way and who determines that? The tenants have to wash clothes and all. Now what if they don't use too much water? The fee stands? They are paying enough already with fees and any damages. It sounds like greed pure and simple.

HOA's and owners and renters - what a mess the spider web has become - at one time HOA's were a good thing. Just like the union's in the beginning helping the workers out and look at it now, who knows - with the paying membership /owners and the CCR's with bylaws it seems like something good at one time is now run amuck

Our condo has hired a management company for all owners. They want to charge owners who rent in order to pay for the management company. Is this discrimination?